Your best bet would be to find out who flies non-stop from your airports and go with their card.
Living near Phila., I have choice of either USAirways or AirTran. AirTran does not have a frequent flier rewards card so the decision is easy for me.
My USAirways VISA is a platinum card and is issued by Bank of America. The annual fee is $40. They reward 1 ff mile for each $ spent with double miles for purchases at their partners (National Car Rental. 1-800-Flowers, etc.) Every December they send a voucher with your statement that entitles you to up to 2 companion fare tickets for $90 when you book a flight that costs $300 or more within the continental US.
A roundtrip ticket within the continental US will cost you 25,000 miles. That means that you would have to charge more than $2,000 per month for a year to get just one ticket. And you'll pay a fee to have the ticket processed and don't forget the 9-11 tax which isn't covered.
Also, there are only a set number of seats available on each flight for frequent flier tickets. You may not be able to get your whole family on a flight for free, even if you have enough miles. Blackout dates also apply. I'm considering dropping the card b/c of the annual fee and restrictions on the flight availability.
I have a Chase-i card and I get $10 in Webcertificates for every $1,000 spent. That's $250 in webbies for every $25,000, which is what I would have to spend to get a free flight. For $250, I can get a ticket for myself and still have money left over. Plus, I don't have to be limited to whatever flights the airline has available to frequent fliers. I can book my own flights, whenever I want. Plus, there is no annual fee.
There are other cashback cards out there that give more back but only on an annual basis. The Chase-i webbies are sent every time your total charges exceed $1,000. So if your monthly charges are $1,786 then you get an $18 webbie that month. If your charges are $822 then that amount rolls over to the next month and the amount continues to acrue until you do go over $1,000 in charges.
I don't want to talk you out of getting an airlines' credit card but keep in mind that there are restrictions on frequent flier miles usage and that those miles are worthless anyplace else. You may also be getting a better deal with a Discover Card or American Express rebates card.