My experience is that Discover has the best customer service of any card I use (if that's not damning with faint praise.)

Discover rewards are denominated in dollars, which makes them harder to devalue than points. So there, CitiBank! Their quarterly rewards promos are worthy. So are their reward partners: The partners offer value cards for greater than 1 to 1 ratios: Blockbuster 3/2, Samsonite 2/1, Crutcfield 5/4.

They haven't lowered my credit limit yet, but they have raised interest. I'm a freeloader - I pay in full, so I don't really care. Discover has the longest grace period of any of my cards, and they usually get me the bill in 4-5 days of closing instead of the week or more that Amex and the others take.

That said, every year or so they miscalculate my rewards - always in their favor - just to see if I'm paying attention. Always resolved in my favor in one reasonably brief phone call. Use the instructions at gethuman.com to bypass telephone tree hell.