As the other poster stated, the loyalty programs are very similar nowadays but one option to consider, in addition to credit cards where you can earn miles, many airlines offer debit cards with checking account. Many airlines also offer miles earned when purchasing things like flowers, dinner, etc.
Usually it takes about 25,000 miles to get a free flight.
Really, all the credit card programs are pretty much the same--- interest and fees are almost identical, and almost all the airlines charge the same amount of miles for you to get your free tickets. Blackout dates are the same, availability is pretty similar across the airlines. So the "best" airline awards card is the one that gets you the rewards you want. If you want to save your miles for a free domestic trip, look at which airlines fly the best schedules to your favorite destinations from your favorite home airport. For example, I live in DC, very close to National Airport where USAir has a ton of non-stops. So I chose USAir's program. I could have picked United but United has few nonstops out of National; I would have to go to Dulles (an hour away) or take connecting flights. No thanks! If you live near Dallas, you may want to look at AA because they pretty much own DFW; if you're in Atlanta, Delta is your best bet. And so forth.
If you want to save up for International travel, look at who has partner airlines that fly to where you want to go. If you want to go to Italy, you could pick NWA because they partner with Alitalia.
Basically, you want to make it as easy as possible for you to redeem the miles for flights you actually want to take. It does you no good to have 100,000 miles with USAir if you need to take 3 planes between Atlanta and NYC to get your free flight.
no.. it depends what airline.. like... there all mostly the same.. but if u want a airline that is cheap to get more skymiles and stuff.. id say jetblue or what ever u prefer for an airline.