I'm currently "stuck" with 4 different cards, AMEX Blue for Students, Delta Platinum AMEX, Citi Dividend Visa and Mastercard.

In comparing the three, the BEST rate comes from, oddly enough, the Platinum AMEX, 2% built in. Citi decided to change the T+C on me last year and charge me a chunk at the end of the month in foreign fees, not so great at all. AMEX is a 2% fee verus a 3% fee for the Citi cards. I would prefer getting the cash back (5% at gas stations, grocery stores and drug stores and 1% everywhere else) but I only use it at the places that I get 5% back.