Short answer — the Sri Lankan credit cards most consistently offering the strongest merchant discounts, seasonal campaigns and partner deals are (in no particular order):

• SampathCards (Sampath Bank) — large seasonal campaigns (Avurudu and year‑round partner discounts, advertised up to ~60% at partner merchants). (dailynews.lk)
• Commercial Bank (ComBank) credit cards — very large merchant network seasonal promotions (thousands of partner outlets, discounts up to ~50–60% during Avurudu / year‑end campaigns). (mawratanews.lk)
• NDB Bank credit cards — frequent merchant tie‑ups, advertised big seasonal savings (reports of up to 60–70% at selected merchants during campaigns), plus regular instalment/0% plans and supermarket/hotel dining tie‑ups. (ceylontoday.lk)
• Nations Trust Bank (Mastercard / American Express) — frequent merchant offers (dining, retail, electronics, travel) and many targeted AmEx/NationsTrust regional offers. Good for AmEx‑specific partner deals. (nationstrust.com)
• HSBC (Live+/Rewards) — steady restaurant, hotel and lifestyle partner discounts (Live+ dining offers and merchant discounts; note: changes can occur if bank ownership/strategy changes). (HSBC.lk)

Why these make the list

• Scale of merchant network and regular seasonal campaigns (Sampath, ComBank) — these banks run island‑wide, high‑visibility seasonal promotions with many merchant partners and highest headline discounts. (dailynews.lk)
• Year‑round partner deals + instalment plans (NDB) — NDB combines deep seasonal discounts with recurring supermarket, dining and hotel offers and flexible instalment promotions that effectively increase value. (ceylontoday.lk)
• Card brand partner strength (AmEx at Nations Trust; Mastercard/Visa partnerships) — certain cards unlock AmEx‑only or brand‑specific merchant lists that can deliver higher savings at select merchants. (americanexpress.lk)

How to pick the best card for “merchant offers”

• Match card to your spending categories: choose the bank/card that runs biggest offers where you spend most (dining, supermarkets, travel, electronics, fashion).
• Look for seasonal campaign timing: some banks lead major seasonal campaigns (Avurudu, year‑end) — if you plan big spending in those periods pick that bank. (dailynews.lk)
• Check instalment / Easy Payment Plan options — cards that offer 0% instalments or long EMI plans at partner merchants can be more valuable than headline discounts. (ceylontoday.lk)
• Consider card brand (AmEx vs Mastercard/Visa) — AmEx often has separate merchant offers not available to Visa/Mastercard cards. (americanexpress.lk)

A practical checklist (quick steps)

1. Check the bank’s “Offers/Promotions” page for the card you already have (or plan to apply for). Bank pages list participating merchants, dates and maximums. (dailynews.lk)
2. Compare whether discounts are instant at checkout, capped per transaction, or provided as statement credits.
3. Confirm required transaction currency (LKR vs foreign), minimum spend and blackout dates.
4. If you want AmEx‑level merchant deals, check Nations Trust’s AmEx offers; for broad island coverage check Sampath, ComBank and NDB. (americanexpress.lk)

Notes and cautions

• Offers change frequently (seasonal campaigns, merchant lists and expiry dates). I used published 2025 campaign reports and bank offer pages — always verify the current offers on the issuing bank’s official website or by calling their card centre before relying on a deal. (dailynews.lk)
• If you want, I can check current live offers for a specific bank or specific card (e.g., “ComBank Visa Platinum”, “Sampath Platinum”, “NDB Visa Infinite”, “Nations Trust AmEx”) and list active merchant partners and expiry dates — tell me which card(s) to look up and I’ll fetch the live promotion pages and cite them.

Sources (examples I used)

• SampathCards Avurudu campaign coverage. (dailynews.lk)
• Commercial Bank (ComBank) Avurudu / seasonal discount reports. (mawratanews.lk)
• NDB credit card offers / seasonal and instalment features. (ceylontoday.lk)
• Nations Trust Bank Mastercard / American Express offers pages. (nationstrust.com)
• HSBC Live+ dining offer page (example). (HSBC.lk)

If you want — tell me the categories you care most about (dining, supermarkets, fashion, electronics, hotels) or name 2–3 specific cards and I’ll pull the current merchant offers and expiry dates for each and summarize which gives the best practical value right now.