+1 As someone who formerly put 100K per year on both AA and UA and then decided a few years ago to concentrate on AA because UA was going so far downhill, I've been very happy with that move and haven't looked back. Shorter security lines, a nicer terminal and better upgrade chances into and out of SFO on AA (partly because of the overall AA frequent flyer program and, ironically, partly because SFO is a UA hub and therefore you have much more competition for upgrades). Plus right now AA's FF program and overall operations are superior. Some very nice redemption options, particularly to Asia on CX F or J.

Now, having said that, the FF field is a moving target these days and it seems that once the AA merger/integration with US is complete its FF program and perhaps other aspects of the airline will go downhill. Plus recent rumblings from CX make it unclear for how long the pretty good AA access to CX award flights will remain pretty good.

For other, more focused feedback, you might add if there are any particular destinations in the US and abroad you're likely to be going to frequently, as that could influence folks' advice. But in the absence of UA and its partner airlines being much better for those destinations (and perhaps even if they are better), I'd still suggest AA.