I'm a little surprised no one has recommended the Starwood Starpoints Amex. It is usually regarded as the best cc deal going. Positive points:

1. It's an Amex (Debatable point, but ero2 has a preference for it.

2. More flexibility--your points accrue in an account that is independent of any one airline. You can easily transfer them to many airlines (including DL and AA) and they give you a 5k bonus for transferring 20k points. So you are getting 1.25 miles per $ spent.

3. Use of the card extends the expiration date of the points--no need to stay in a Starwood hotel. Also, in these days of airline financial woes, hotel programs are considered to be a safer bet for retaining the value of points--if AA goes under you still have something of value.

4. Low annual fee (especially for Amex)--only $30 (up until a couple of years ago it was free.

5. They always have some signup bonus going (usually 7500 to 10,000).

I use this card as my primary and also have the Citi AA Mastercard as a backup. In the interest of full disclosure I used to be a Delta flyer (this will be my last year with status) and had the Delta Amex also. But since I became disgusted by Delta's ultra-restricitve policies on just about everything I've switched to fly AA almost exclusively--for all of the reasons others have mentioned. No regrets. Also, I found the fee on the Delta Amex to be excessive and the bonus offers to be difficult to take advantage of (spend on the weekend, only certain stores--some but not all grocery stores, etc.). I was never sure if I ever got it right. Kudos to all of you who have!