Singapore to KL vs Penang vs JB vs Melaka 2026: Cheapest Way to Each

The Singapore-to-Malaysia 4-way land and air framework, 2026

Singapore residents crossing into Malaysia in 2026 have four distinct destination shapes and four distinct optimal routes:

• JB (30 minutes away): causeway or Second Link land crossing at S$0 to S$18 today; the RTS Link has not opened yet.
• Melaka (155 km / 3.5 hours drive): direct coach at S$25 to S$45, 5 to 6 hours end to end.
• KL (355 km / 4.5 hours drive): coach at S$28 to S$55, ETS train from JB Sentral at S$28 to S$68 (5 to 6 hours total), or AirAsia flight at S$68 to S$180 (2 to 3 hours door to door).
• Penang (700 km / 8+ hours drive): AirAsia direct flight at S$75 to S$240, 1h 25min flight plus door to door 3 hours.

This guide picks the cheapest reliable option for each, adds time cost, currency and border reality, and shows how to go through ShopBack Singapore before you pay on Trip.com, Klook, Agoda, and Booking.com bookings.

The 4-destination at-a-glance

Destination	Cheapest option	Fare (S$)	Total time	Second-cheapest	Best for
JB	Cross-border bus / SBS 170	S$1 to S$5	30-90 min	Coach S$5-S$18	Day trip, hawker food, KTV, spa
Melaka	Direct coach	S$25 to S$45	5-6 hours	Drive (with VEP)	Weekend heritage, food
KL	Direct coach	S$28 to S$55	5.5-7 hours	AirAsia flight S$68-S$180	Weekend or long weekend
Penang	AirAsia flight	S$75 to S$240	3 hours door to door	Coach via KL (12-16 hr)	Weekend heritage, food

Sources: SBS Transit, Causeway Link, Transtar, Aeroline, 707 Coach, KTMB ETS, AirAsia, Scoot route pages, verified September 2026.

JB: causeway, Second Link, and the RTS Link countdown

JB is the shortest and cheapest of the four destinations in 2026. The three current options:

Cross-border bus (SBS 170, 950, Causeway Link CW1, CW2): S$0.90 to S$5 one way, 20-90 minutes total including immigration depending on peak. Best on weekdays 10am to 4pm to avoid queue chaos. Weekends and public holidays regularly hit 2+ hour waits at Woodlands during peak.

Private car via causeway: Requires VEP-enrolled Singapore vehicle, subject to Malaysian toll and Singapore VEP RFID. Peak weekend congestion adds 90 to 180 minutes to the crossing. Second Link at Tuas is typically 30 to 60 minutes faster on peak days.

Coach direct: S$5 to S$18 one way from Golden Mile Tower, Kranji, or Boon Lay to Larkin Sentral or Wisma MBSJ. Often faster than driving on peak due to dedicated bus lanes and coach-priority immigration lanes at Woodlands and Tuas.

RTS Link countdown: The Rapid Transit System Link between Woodlands North MRT and Bukit Chagar station in JB had not opened at the time of writing; check the Land Transport Authority site for the confirmed opening date. Once RTS opens, the crossing time compresses to roughly 5 minutes plus immigration. Until then, the current options apply.

Book through ShopBack: JB day-trip hotel bookings (typically S$50 to S$140 per night for Karafuru-tier or KSL Resort) route through Agoda or Booking.com via ShopBack Singapore. Klook covers Legoland Malaysia and Puteri Harbour attractions; go through Klook on ShopBack Singapore before you pay.

Melaka: the 5-hour coach that wins on price and time

There is no direct commercial flight from Singapore to Melaka Airport (which handles limited domestic Malaysian routes only). There is no direct rail service; the ETS train stops at Tampin, 40 minutes by taxi from Melaka historic centre. The direct coach is the only reliable option.

Coach routes: Delima Express, KKKL, Konsortium, and Transtar run 6 to 10 daily departures from Golden Mile Tower and Boon Lay to Melaka Sentral. Fares S$25 to S$45 one way, 5 to 6 hours end to end including border clearance and comfort stops. Morning departures (6-9am) get you into Melaka by lunch; late afternoon (2-5pm) departures put you in Melaka for dinner.

Drive alternative: Singapore-registered VEP-enrolled car via Second Link, 3.5 to 4.5 hours one way. Adds fuel and toll (RM 30 to RM 45 one way) plus VEP RFID compliance.

Book through ShopBack: Book the coach ticket through Klook via ShopBack Singapore, or direct with the operator. Melaka boutique heritage hotels (Majestic Malacca, Casa del Rio, Hotel Puri, The Sterling) run S$85 to S$220 per night on Agoda or Booking.com; both platforms are on ShopBack Singapore. Klook covers Melaka River Cruise, A'Famosa Resort, and food tour vouchers.

KL: coach, ETS train, or AirAsia flight

KL is the most-choice destination among the four, with three viable transport options in 2026.

Direct coach (5.5 to 7 hours, S$28 to S$55): Transtar, Aeroline, StarMart Express, 707 Coach, and Konsortium run 12 to 20 daily departures from Golden Mile Tower and Boon Lay to Bandar Tasik Selatan or KL Pudu Sentral. Aeroline offers a first-class-style seat with lounge access at Kuala Lumpur for S$60 to S$90 one way. Overnight sleeper coaches (10pm to 5am) save one hotel night on either end.

ETS train from JB Sentral to KL Sentral (5 to 6 hours total, S$28 to S$68 plus S$5-S$10 to JB): Cross the causeway to JB Sentral, board ETS Gold or Silver, arrive at KL Sentral in 4h 15min. Ticket price on ETS Gold is MYR 79 to MYR 139 (S$23 to S$41) one way; book via KTMB portal, 12Go Asia, or Klook 30 days ahead for the widest availability. Scenic through the palm oil and rubber belt of Johor and Negri Sembilan.

AirAsia or Scoot flight (45 min flight, 2 to 3 hours door to door, S$68 to S$180): 15+ daily Singapore Changi to KLIA departures. AirAsia is the cheapest on most days; Scoot competes on select time slots. Malaysia Airlines and Firefly (via Subang) offer full-service options at S$120 to S$260.

Book through ShopBack: Book the coach via Klook, the ETS on the KTMB portal or via Klook, and flights via Trip.com or Expedia, going through the ShopBack Singapore store page before you pay for the Klook, Trip.com or Expedia booking. KL hotels, usually the biggest single booking of the trip, go through Agoda or Booking.com on ShopBack.

Penang: AirAsia direct wins on time and often on cost

Penang is 700 km from Singapore, and there is no efficient overland option in 2026. The KTMB ETS via KL adds 12 to 16 hours total travel time versus a 1h 25min direct flight. AirAsia direct from Changi to Penang International Airport wins on almost every axis.

AirAsia and Scoot Changi to Penang: several daily departures across the carriers in 2026, one-way fares S$75 to S$240. Fares are usually lowest in months inside Singapore school terms with no long weekend, such as mid-January, April, July and mid-September to late October. Peak periods are Hari Raya, the June and year-end school holidays, and Chinese New Year week.

Firefly and Malaysia Airlines: Firefly flies Subang (Kuala Lumpur secondary) to Penang, requiring a Singapore-KL leg first. Malaysia Airlines flies KL to Penang with codeshare on some Singapore-KL flights. Not competitive on a Singapore direct basis.

Overland via KL: For the adventurous: coach or ETS Singapore to KL (5 to 7 hours), then ETS Gold KL to Butterworth (4 hours), then Penang Ferry Services or Penang Bridge to George Town (30 min). Total 12 to 16 hours, roughly S$65 to S$110 one way. Only for travellers who value the journey over the destination.

Book through ShopBack: Book AirAsia or Scoot via Trip.com or Expedia through ShopBack Singapore. George Town heritage hotels (E&O Hotel, Cheong Fatt Tze Blue Mansion, Seven Terraces) on Agoda or Booking.com through ShopBack. Klook covers Penang Hill funicular, ESCAPE Theme Park, and food tour vouchers.

Border and immigration reality in 2026

• Woodlands Checkpoint: 24-hour operation, extended peak (Friday 3-9pm, Saturday and Sunday all day, public holiday eves). Malaysian side (BSI) closes bus lane periodically for security.
• Tuas Checkpoint (Second Link): 24-hour operation, less congestion than Woodlands on peak but longer detour if your Singapore or Johor start point is not near Tuas.
• Auto-clearance: Singpass-enrolled Singapore citizens use the QR eGate at both Woodlands and Tuas. MyDigital ID Malaysian nationals use eGate on Malaysian side. Non-enrolled foreigners must use manual counters.
• Land arrival card: Most foreign visitors must submit the free Malaysia Digital Arrival Card (MDAC) online before arrival. Singapore citizens are exempt; other Singapore residents should check the current rules at imigresen.gov.my.

SGD to MYR: multi-currency card is best

Multi-currency cards (YouTrip, Wise, Revolut) convert at close to interbank rate with no markup for MYR. Singapore money changers (Mustafa, Change Alley, Arcade) sit 0.3 to 0.6% below interbank. Singapore-issued credit cards apply a 2.8 to 3.25% FX markup, worst option for in-Malaysia daily spend.

For online prepay bookings on Agoda, Booking.com, Klook and Trip.com through ShopBack Singapore, the credit card FX does not apply because the booking is in SGD from a Singapore platform. Pay with your DBS Live Fresh, OCBC 365, UOB One, or HSBC Revolution card for the parallel card cashback on the SGD leg.

Using ShopBack on Singapore to Malaysia trips

Across the four destinations, go through ShopBack Singapore before you pay for:

1. Flights to KL, Penang, or JB via Trip.com or Expedia through ShopBack.
2. Coaches and ETS trains via Klook through ShopBack.
3. Hotels in JB, Melaka, KL, or Penang via Agoda or Booking.com through ShopBack.
4. Attractions (Legoland, Penang Hill, KL tower, Melaka River Cruise, A'Famosa) via Klook or Kkday through ShopBack.
5. Airport transfers in KL, Penang, or JB via Klook through ShopBack.

The workflow is the same each time: open ShopBack Singapore, search for the platform, click through to the merchant page, complete the booking in the same session. Cashback confirms on each store's own timeline, shown on its ShopBack page.

How can I find cheap flights from Singapore to Penang?

The cheapest Singapore to Penang flights usually come from a direct low-cost fare on a Tuesday, Wednesday or Thursday, booked about one to two months ahead and outside Singapore school holidays and long weekends. The direct flight from Changi to Penang International Airport takes about 1 hour 25 minutes, so there is rarely a saving in routing through KL, and the overland options above take 12 to 16 hours. Finding the low fare on this route comes down to five habits.

1. Search a whole month, not one date. Open the flexible date or calendar view on the booking site and scan a full month of Singapore to Penang fares before you fix your dates. On a short route like this, moving a departure by one or two days often matters more than which site you book on.

2. Compare the total, not the headline fare. Low-cost fares on this route often leave out checked bags and seat selection. Add the bag you actually need before you compare. A fare that looks S$15 cheaper can end up costing more once a 20kg bag is added at checkout.

3. Price the same flight on two or three sites. The same AirAsia or Scoot flight can show slightly different totals on Trip.com, Traveloka and Expedia because of service fees, baggage bundles and member pricing. Compare in SGD so currency conversion does not hide the gap.

4. Stay off the peak calendar. Singapore's year-end school holidays run from Saturday 21 November to Thursday 31 December 2026, according to the Ministry of Education's academic calendar. Deepavali falls on Sunday 8 November 2026, with Monday 9 November as the day off in lieu for most workers, according to the Ministry of Manpower. Penang fares around those dates usually climb as families and long-weekend travellers book.

5. Book the flight and the hotel as two separate bookings. On Trip.com, flight plus hotel bundles and packages are excluded from ShopBack, according to the Trip.com terms on ShopBack Singapore, while a flight and a hotel booked separately each qualify. Splitting them also lets you pick the best George Town hotel price on Agoda or Booking.com rather than the bundled hotel.

Plan the trip, then book through ShopBack. Once you have picked your Penang flight, open the Trip.com page on ShopBack, the Traveloka page on ShopBack or the Expedia page on ShopBack and click through to book in that same session.

Trip.com vs Traveloka vs Skyscanner for Singapore to Penang flights

Neither Trip.com nor Traveloka is always cheaper for Singapore to Penang. Both sell flights on the route priced in SGD, and on the same flight the difference is usually small, coming from service fees, baggage bundles and member or sale pricing. Trip.com shows some member prices only when you are signed in, and Traveloka runs its own app sale events through the year, so it is worth checking both on the day you book.

Skyscanner does a different job. It is a fare search engine: it compares prices across airlines and booking sites and then sends you to one of them to pay. It is useful for spotting the cheapest week, after which you can price that exact flight on Trip.com, Traveloka or Expedia and book wherever the final total, with bags, is lowest.

One rule matters more than which site wins. According to ShopBack Singapore's terms for Trip.com and Traveloka at the time of writing, using a promo, coupon or discount code makes the order ineligible on ShopBack. So compare what the code saves against what ShopBack returns before you apply one.

What is the cheapest month to fly from Singapore to KL?

Singapore to KL fares are usually lowest in months that sit inside Singapore school terms and have no long weekend. Over the next twelve months that usually points to mid-January, April, July, and the weeks from mid-September to late October. Fares usually climb in the year-end school holidays, over Chinese New Year and around Hari Raya, when both Singapore families and Malaysians heading home are booking the same flights.

Because flight prices move daily, the most reliable guide is the official holiday calendar rather than a fixed list of cheap months. These are the dates that usually push Singapore to KL fares up, according to the Ministry of Education and the Ministry of Manpower:

Period	Dates	Why fares usually rise
Deepavali long weekend	Sun 8 Nov 2026 (Mon 9 Nov off in lieu)	Long weekend demand
Year-end school holidays	Sat 21 Nov to Thu 31 Dec 2026	Family travel peak
New Year's Day	Fri 1 Jan 2027	Long weekend demand
Chinese New Year	Sat 6 and Sun 7 Feb 2027 (Mon 8 Feb off in lieu)	Long weekend and family travel
Hari Raya Puasa	Wed 10 Mar 2027	Festive travel in both countries
Good Friday	Fri 26 Mar 2027	Long weekend demand
Hari Raya Haji and Vesak Day	Mon 17 May and Thu 20 May 2027	Long weekend demand
National Day	Mon 9 Aug 2027	Long weekend demand
Deepavali	Thu 28 Oct 2027	Bridge holiday demand

Sources: Ministry of Manpower public holidays page and Ministry of Education academic calendar, checked October 2026. MOE's 2027 school holiday dates were not yet listed when we checked; in 2026 the school holidays fell in mid-March, from late May to late June, in early September and from late November to year end, and the pattern is usually similar each year.

How to use the calendar when booking Singapore to KL

Pick a midweek departure in a month with no holiday on this list, then open a whole-month view on a fare search engine or booking site to see which week is cheapest. With 45-minute flights and many daily departures between Changi and KLIA, the cheaper days usually sit within a few dollars of each other in a quiet month, while a holiday week can be noticeably dearer. If the flight still looks expensive, the coach and the ETS train from JB Sentral, covered above, are usually the cheapest ways to KL on the ticket price.

Skyscanner vs Trip.com for Singapore to KL flights

Use Skyscanner to search and Trip.com, Traveloka or Expedia to book. Skyscanner compares fares across many sites and hands you over to one of them to pay, so it is a quick way to see the cheapest week. Trip.com is the booking site where the ticket is issued. Once you know the week, price the exact flight with your bags on two booking sites and pay on whichever is lowest, going through ShopBack first.

Booking Singapore to Penang and KL flights through ShopBack

ShopBack is a post-purchase discount: go through it before you pay and the effective price drops. Cashback lowers what you actually pay for an order. It comes back as cash, so it works like a discount on the price, not like points or miles.

Check the live rate for each store on its ShopBack page before you pay: Trip.com, Traveloka and Expedia.

A few store rules to know before you pay, according to the terms on each ShopBack Singapore store page at the time of writing:

• Trip.com: Promo, coupon, or discount codes make your entire Trip.com order ineligible for Cashback. Flight plus hotel bundles and packages, child and infant flight tickets, and baggage or meal purchases are also excluded.
• Traveloka: promo code or coupon usage is not eligible, and the Flight + Hotel category is excluded. Only purchases made in SGD are eligible.
• Expedia: purchases made with vouchers or promo codes not featured on ShopBack are excluded, as are store credit redemptions.

The order of steps is simple. Choose your dates using the calendar above, compare the flight on two sites, then open ShopBack, tap through to the winning store and pay in that same session without switching browsers.

Frequently asked questions

What is the cheapest way to get from Singapore to KL in 2026?

The cheapest reliable Singapore-to-KL route in 2026 is the coach direct from Golden Mile Tower or Boon Lay to Bandar Tasik Selatan in KL. Fares on Transtar, Aeroline, StarMart Express, and 707 Coach range from S$28 to S$55 one way (5.5 to 7 hours end to end including border clearance). Second-cheapest is the AirAsia or Scoot flight from Changi to KLIA, currently S$68 to S$180 one way (45 minutes flight, plus 3 hours end-to-end door to door). The ETS train via JB Sentral to KL Sentral is S$28 to S$68 (5 to 6 hours), requires a causeway crossing to JB Sentral first, and is best for travellers who want the scenic option. Book coaches via Klook, and flights via Trip.com or Expedia, going through ShopBack Singapore before you pay.

What is the cheapest way to get from Singapore to Penang in 2026?

AirAsia direct from Changi to Penang International Airport is the cheapest and fastest reliable route in 2026, at S$75 to S$240 one way for a 1h 25min flight. Scoot also flies the route with similar pricing. Ground alternatives (coach via KL, or KTMB train via JB and KL) take 12 to 18 hours and cost S$65 to S$110 one way, so the flight wins on total time and often on cost after factoring meals and airport transfers. Book flights via Trip.com or Expedia, going through ShopBack Singapore before you pay; airport transfers to and from Bayan Lepas via Grab or Klook shuttle add S$18 to S$35.

When does the RTS Link between Singapore and JB open?

The Rapid Transit System (RTS) Link between Woodlands North station in Singapore and Bukit Chagar station in Johor Bahru had not opened at the time of writing; check the Land Transport Authority site for the confirmed opening date. Until it opens, the Singapore to JB options remain the SBS Transit or Causeway Link cross-border bus (S$0.90 to S$5, 20-45 minutes at causeway plus border), private car via the causeway (subject to VEP requirement and toll costs), and coach via the Second Link at Tuas (typically 30 to 60 minutes faster on peak days than the causeway). Once RTS opens, the crossing time compresses to roughly 5 minutes plus immigration. For JB hotel bookings, go through Agoda on ShopBack Singapore before you pay.

How long is the coach from Singapore to Melaka in 2026?

The direct coach from Singapore to Melaka Sentral takes 5 to 6 hours end to end including border clearance and comfort stops, at fares of S$25 to S$45 one way. Operators include Delima Express, KKKL, Konsortium, and Transtar. Departures cluster in early morning (6-9am from Golden Mile Tower or Boon Lay) and late afternoon (2-5pm) with return trips in the reverse pattern. There is no direct rail service from Singapore to Melaka; the ETS train stops at Tampin, roughly 40 minutes by taxi from Melaka historic centre. There are no direct commercial flights (Melaka Airport handles limited domestic Malaysian routes only). Book the coach via Klook, going through ShopBack Singapore before you pay.

How do I use ShopBack on Singapore to Malaysia land and short-haul flight bookings?

Open the ShopBack Singapore app or Chrome extension first, click through to the platform (Trip.com or Expedia for AirAsia, Scoot, Firefly, and Malaysia Airlines flights; Klook for ETS, coach, and airport transfer vouchers; Agoda or Booking.com for JB, Melaka, Penang, and KL hotels), and complete the booking without switching browsers or opening another cashback or coupon link. ShopBack tracks the click and confirms Cashback on each store's own timeline, shown on its ShopBack page. The current cashback rate for each platform is shown on the ShopBack merchant page and moves with promotional periods.

Is the ETS train from JB Sentral to KL Sentral cheaper than flying in 2026?

Yes on the ticket, but total door-to-door time and hotel-value math often favours the flight. ETS Gold from JB Sentral to KL Sentral is MYR 79 to MYR 139 (S$23 to S$41) one way for a 4h 15min journey; add S$5 to S$10 to reach JB Sentral from Singapore, and 5.5 to 7 hours total including border. AirAsia Singapore Changi to KLIA is S$68 to S$180 one way for a 45-minute flight, plus 2 to 3 hours door to door including airport transit. ETS wins on price for budget travellers and delivers a comfortable seated journey with wifi. Flight wins for time-value and business travel. Book ETS on the KTMB portal or Klook, and flights on Trip.com or Expedia; for Klook, Trip.com and Expedia, go through ShopBack Singapore before you pay.

Do I need a Vehicle Entry Permit (VEP) to drive from Singapore into Malaysia in 2026?

Yes. All Singapore-registered private vehicles entering Malaysia require a valid VEP with a working RFID tag installed on the windscreen, enforced by JPJ (Malaysian Road Transport Department). Registration is done online through the JPJ portal ahead of the first trip; the RFID installation is done at a JPJ-approved centre in Woodlands or JB. Non-compliant vehicles face RM 300 to RM 2,000 fines. For rental cars from Malaysia, the rental company handles the VEP. For the Malaysia hotel booking, go through Agoda or Booking.com on ShopBack Singapore before you pay.

What is the cheapest month to fly Singapore to Penang or KL in 2026?

Singapore to KL and Penang fares are usually lowest in months that sit inside Singapore school terms and have no long weekend, such as mid-January, April, July and mid-September to late October. Fares usually climb in the year-end school holidays (21 November to 31 December 2026, according to MOE), over Chinese New Year (6 and 7 February 2027, according to MOM) and around Hari Raya Puasa (10 March 2027, according to MOM). Set fare alerts 8 to 10 weeks out, then go through Trip.com or Expedia on ShopBack Singapore before you pay.

How much is a JB weekend from Singapore in 2026 including hotel and food?

For 2026, a Friday-to-Sunday JB weekend from Singapore lands at S$180 to S$380 per person all-in. Cross-border bus each way is S$5 to S$20; a Karafuru-tier or KSL hotel 2-night stay booked through Agoda or Booking.com via ShopBack Singapore runs S$90 to S$220; food across 3 days at Malaysian prices (nasi lemak breakfast, seafood or KL-style lunch, Sedap Malay dinner) totals S$60 to S$110; shopping and massage add another S$40 to S$80. If you drive, add the VEP-enrolled Singapore-registered fuel and toll cost (RM 20 to RM 60 round trip). The hotel is usually the largest single booking, so go through Agoda or Booking.com on ShopBack before you pay for it, then go through Klook on ShopBack for Legoland or theme park tickets if included in the plan.

Is the SGD to MYR conversion better in cash, credit card, or multi-currency card in 2026?

For 2026, multi-currency cards (YouTrip, Wise, Revolut) deliver the best SGD-to-MYR conversion at close to the interbank rate with no FX markup and no minimum. Cash from Singapore money changers (Mustafa, Change Alley) is second-best at 0.3 to 0.6% below interbank. Credit cards from DBS, OCBC, UOB, HSBC, SCB, Citi apply a 2.8 to 3.25% FX markup, which is the worst option for MYR spend inside Malaysia. Use a multi-currency card for daily MYR spend and keep a Singapore credit card for online prepay bookings on Agoda, Booking.com, Klook, and Trip.com through ShopBack Singapore, so you earn ShopBack Cashback and your card's own reward on the online bookings.

How can I find cheap flights from Singapore to Penang?

Search a whole month of Singapore to Penang fares rather than one date, favour Tuesday to Thursday departures, and book about one to two months ahead outside Singapore school holidays and long weekends. Compare the same flight on two or three booking sites such as Trip.com, Traveloka and Expedia in SGD, with the checked bag you actually need added, because low-cost fares on this route often leave bags out. The direct flight takes about 1 hour 25 minutes, so routing through KL rarely saves money. Once you have picked the flight, go through ShopBack to the booking site before you pay so the effective price drops.

What is the cheapest month to fly from Singapore to KL?

Singapore to KL fares are usually lowest in months that sit inside Singapore school terms and have no long weekend. Over the next year that usually means mid-January, April, July and the weeks from mid-September to late October. Fares usually climb in the year-end school holidays (21 November to 31 December 2026, according to MOE), over Chinese New Year (6 and 7 February 2027, according to MOM) and around Hari Raya Puasa (10 March 2027, according to MOM). Prices change daily, so check a whole-month view before you fix your dates.

Is Trip.com or Traveloka cheaper for Singapore to Penang flights?

Neither is always cheaper. Both sell flights on the Singapore to Penang route priced in SGD, and on the same flight the difference is usually small, coming from service fees, baggage bundles and member or sale pricing. Price the exact flight with your bags on both, plus Expedia if you like, and book wherever the final total is lowest. According to ShopBack Singapore's terms for each store, using a promo, coupon or discount code makes the order ineligible on ShopBack, so weigh the code saving against what ShopBack returns before you apply one.

Should I use Skyscanner or Trip.com to find cheap Singapore to KL flights?

They do different jobs. Skyscanner is a fare search engine that compares prices across airlines and booking sites, then sends you to one of them to pay. Trip.com is a booking site where the ticket is issued. A sensible routine is to use a whole-month view to spot the cheapest week for Singapore to KL, then price that flight on Trip.com, Traveloka or Expedia and book through ShopBack before you pay.