I switched my earning to AA about 8 or so years ago when I realized that AA allowed you to earned lifetime elite status based on all miles earned, not just those earned while flying. I earned Lifetime gold (1 M miles) about 4 years ago and expect to earn Lifetime platinum (2M miles) in about a year.
With elite status comes faster check in, faster security lines in some ariports, free checked luggage for your party, ability to stand-by, some free upgrades, and earlier boarding.
My favorite way to earn is with the Starwood Preferred Guest Amex. With this card, each time you charge $20,000, you can convert it into 25,000 AA miles. SPG points can also be converted into other programs: my parents used their points for discounts on Virgin Upper Class to London when travelling on the
DCL Baltic cruise last summer and I have used points for Amtrak rewards to travel to DL. Look for a bonus when sigining up; they offered as many as 30,000 points last year.
I also have a Citibank AA MC. Generally, one mile for each $, although I sometime get bonus offers. I beleive Citibank has a very good sign up offers right now of as much as 75,000 miles.
We usually use the AA miles for upgrades to FC on cheap coach fares. -- Suzanne