The best advice I can give is to invest some time in these forums and read the blogs. Almost anything you could want to know is in here. You should consider bumping this thread
http://www.flyertalk.com/forum/new-e...o-out-bos.html
I bet a lot of people will share their knowledge and opinions with you.

To your situation, I would stick with USAir, as you already have status. Consider buying up to chairman's preferred (or platinum if money is tight). It should be less than 1000$. With status secure, you could try out AA, Delta or UA since they all offer the international coverage that you want. I am not sure Jet Blue would meet your needs, although the new "mint" suites transcons is a plus.

No one can tell you which of these programs would be best for you (or least bad) since they all have issues right now. For example, AA treats its elite well but may merge with US with big unkowns, Delta has a notoriously bad frequent flyer program but good service and UA (my program) has been dramatically devaluing its elite status, service and award program (flying them seems like Hell's Kitchen right now) but could be on top in a few years.

I think I would try AA if I were in your position. It would be good to feel out their program in case the merger goes through. The one world alliance can get you to Europe to visit BF. You can rack up 100K Avios with British Airways pretty quickly with credit cards right now, which can be useful for short haul awards on AA.

good luck!