I have no experience on American, but I can tell you, American thinks they're GREAT. I've heard from many friends that say American Airlines is arrogant: probably because it's a big airline.
I've flown on United, but that's 5 years ago. They haven't developed into such a big airline as it is today at that time, so the service was quite good. Again from friends: one of my friends has flown on United recently, and he criticised United severely.
Why don't you try British or Virgin?