I fly AA exclusively, with the occasional exception of a AA partner codeshare flight (e.g., Hawaiian, British) to get to my final destination. Of course, all of my flying is for pleasure, so I don't "have" to be anywhere and can "afford" to be selective. If AA doesn't go there at a price I'm willing to pay, I don't go. If there is some place I really want to go (e.g., the Cow Do in EZE), and I can't afford or refuse to pay the outrageous fare, I plan early and get an award ticket.

The only other exception is that I do collect UA miles (with my Chase Visa check card and grocery miles) and every few years, I get a UA award ticket.