I recently flew AA LAX-MIA-LAX and I can't say AA is better than UA. For one thing, the AA restrooms at LAX are disgusting and the boarding process is a mess. I am intrigued by AA's upgrade policy, it seems to be far superior to UAs.
I am doing a 3 month challenge and will earn Platinum on AA giving me more options next year. If upgrades, even paid 500 miles, are much easier to come by, I may switch for good.