As a 1K on UA and a plat on AA, I am able to compare both airlines, and I believe that both do a pretty good job of what they are suppose to do, which is to get me where I am going on time and in one piece.
While I don't fly international with AA (unlike UA), I do domestic and as far as I am concerned, time and price are the two criteria for me (in that order). Both airlines allow me to same day change if necessary, and both will work to put me on alternative flights when things go boing in the night. And I don't expect an upgrade on most of the flights I take which have F seats because I pay for Y and people up front are paying for F. Furthermore, as everyone else has noted, using miles for anything is a lottery experience.
I have actually found domestic AA crews, especially on the commuter flights, to be quite nice and pleasant.
Finally, I know that both airlines track me, because they constantly nudge me when I have a gap in flying with them due to schedules or travel breaks.