I think the point here (perhaps) is that in the past the AAdvantage program would have tipped someone like the OP to stick with AA, despite his changed travel patterns. With the demise of that program, what he's done makes complete sense. If you're going to travel in Y anyway, then AA is one of the less comfortable options and, from BOS, probably one of the less convenient ones. And if you're going to buy F then DL is usually cheaper and more reliable. In general I'd give AA the nod (slightly) for meals in F and (on the LAA planes) more generous room, but that's doesn't overcome the other DL advantages And for overseas the gulf carriers are hard to beat.