I don't know how much it has changed (in terms of service) with UA during the past few years, but having recently flown a range of AA flights (Y, C, and domestic F), I actually enjoyed my overall experience with AA. I had been EXP previously and at that time, I had converted from UA 1K to EXP and realized AA employees were a bit more genuine than UA ones. Of course, with every airline, there are great days and there are really bad days.

As for upgrades, I won't complain if I don't get upgraded as EXP... because upgrade is a 'gift' for being loyal, not an entitlement. I buy Y ticket, I expect to fly in Y. If I get upgraded? Great! If not, it's not the end of the world.