The new WN program will allow this (but not at a good value). The new WN program will make it easy to redeem on any airline (WN will simply buy the seat on anyone).

Difference is how much you have to fly/spend to get that free seat. Go with WN if you want it simple; forget WN and go with AA if you want 3X the free seats for the same flights/$ spent to earn the points.

Virgin American and JetBlue also have very simple programs. Not very rewarding compared to AA though.

American AAdvantage is one of the top value programs in existence, along with United Mileage Plus. I do not recomend Alaska even though they have a lot of partners to redeem on because you cannot mix and match Alaska partners on a single award ticket (unlike American/United). Most of my high value milage redemptions require multiple carriers, making the use of Alaska miles less than ideal. Delta typcially costs 2X the miles compared to AA/UA for international redemptions.