Sounds like UA meets your needs pretty well.

But you won't find yourself flying F much if you start flyings from IAD instead of BWI. Even 1Ks have trouble upgrading there.

Also, you will find little success with international upgrades (much less saver award tix in C) if you try to confirm months in advance. But of course you are probably used to that kind of treatment...

I haven't flown CO in a long time but my impression is that the domestic upgrade program works much better than UAs for lower level elites, and that the reverse is true for international upgrades and free tix. But YMMV.