Best credit card for Airline miles?

I pretty much pay for EVERYTHING on my Credit Cards and pay them off immediately. I'm even the person people come to at the office and ill put their hotels and flights on my card if they give me cash immediately.
With that being said, what is the best Credit Card, airline specific or not, for Travel miles, specifically to be used for airline travel.

I am not loyal to any specific airline, but really all I have around this area is American and Delta, unless I catch a flight to Chicago or St Louis, which I would only do for a budget airline.

Give me some ideas. I have two capital one cards right now, and the amazon chase card, but don't particularly care for the rewards. I have good, but not excellent credit (somewhere between 730-740)