Which of my cards should I use?

Tick the cards in your wallet, then pick a store or a kind of spending. They are ranked by what each earns on that purchase, in dollars per $100 — the same answer the extension gives at a checkout, from the same catalogue of 118 cards.

Nothing you choose here leaves this page: your picks live in the address bar after the #, which a browser never sends to a server — so a link to this page carries them, and nothing else does. How the numbers are worked out.