I like UA over AA because of their alliances.. Star Alliance partners overall have better mileage accrual in discount economy than OneWorld.. most notably, the 30% accrual on Iberia, no transatlantic miles on BA, and spotty accrual on Cathay.

Plus, I still can't get over the fact that flights < 2hrs on AA don't provide any meals in F. That pretty much includes all East Coast flights departing from ORD. Truly pathetic.