I split between UA and AA...more emphasis on UA...for several reasons. My focus is on accumulating miles, not achieve status. I'm sorry...I can already hear the gasps among most of you and probably deservedly so. My wife and I are into quantity of trips vs. quality. Now with one-way award bookings available, we do that a lot depending on schedules.
We are flying next week SNA-LHR via UA and returning on AA. Not only a better schedule on the return, but snagged some off-peak AA seats for far fewer miles. We're doing the same in the fall...LAX-LIH on UA and AA return...better schedule and availability.
I still like UA better overall...better award seat availability generally. I also like E+ option. I've been pretty lucky with AA, but feel availability is not quite up to UA at this time. I'm hoping it'll improve once the merger is completed.