It all depends what your flying patterns are. AA is weak in the direction of Asia/Australia, but if you're redeeming miles in that direction you can choose from Qantas, Cathay, and JAL. I tend to build my miles on domestic and Europe, and spend them in the direction of Asia/Australia. AA is certainly competitive farewise (I have three $337 base fare Europe tickets over the next 4 months).

AA does offer reduced mileage awards through their credit card. SFO-Newark is 17,500 miles this quarter, for instance.

The free domestic upgrade program for top tier flyers, and elimination of "More Room throughout Coach", may have you leaning towards staying with UA, where you might have a better shot at upgrades and more legroom. If you're aiming for 1K, though, AA's equivalent tier offers quite a few benefits, including space available domestic upgrades (I've cleared 49 of 50 requests this year).