Well there seem to be two choices. First are the cards that just give you dollarls back and then the second are award cards.
Personally, I have an older card, the United Visa Select because it gives you 3x miles for trips booked with United or Continental which is great for those of us booking tickets overseas for business travel. With mileage bonuses, you can for instance on a business trip to China get 10K real miles and another 10K bonus for 100K United plus $7K x 3 = 21K for booking. That’s 40K miles for a 10K trip. Not bad at the 1 cent per mile this is 4 cents per mile!