Of course, UA may not be so healthy next year - contracts are up, credit card holdbacks with JPMorgan Chase come up, money is burning, routes are shrinking or given over to subsidiaries or *A codeshares operated by partners... Some folks (e.g Brancatelli) seem to think UA may not remain long on the horizon.
AA provides 2x4

SWUs when you hit top rank, and two for every million miles from any source (except for NA residents who get 500 mile upgrade "stickers" the first M.) I'll stick with that, since it seems to work and no easy lean to bankruptcy in their preferences for problem solving.