It's a tough call. I'm in the US and have memberships in both programs. My travel is 95% international, so I currently fly/earn about 95% BA, but sometimes do burn on AA if I have a domestic vacation (unusual). For the vacation trips I take, I find that BA is the better bet for award tickets. And the BA option of booking one-way award seats is a major, major positive for that program (not sure if AA allows this, but I suspect not). Also, BA Gold is equivalent to AA EXP. If I could get AA EXP with the same flying pattern that I now have, I might consider switching, since AA's mileage earning opportunities are better on Y travel. But I think I'd get bumped down to AA Plat, which is definitely not as good.