If you primarily fly AA (as I do on domestic routes) it does make sense to earn some AAdvantage miles with a credit card. Surprisingly, it turns out that Citi AAdvantage Mastercard is not the best card for earning AA miles. I suggest you investigate the Starwood Preferred Guest credit card, which is also issued by American Express.
Even if you never set foot in a Starwood hotel you should understand the Starwood Preferred Guest Program because it offers the flexibility of a program similar to Membership Rewards with the ability to accumulate AA miles. Used correctly you can earn 25% more AA miles per dollar spent, and have the flexibility to redeem on about three dozen airlines.
I do realize that when one first joins Flyertalk there is genuine information overload. You can't do everything today, this month, or even this year, but keep it in mind for the future.
Thanks for the advice, I will look in to the Starwood CC. I do stay at Starwood a fair amount, enough to earn Platinum with SPG, not sure the amount of days required, but less than Marriott.
I actually joined the board a few years ago, but still feel like there is a lot that I can learn from the members.