So you're an east coaster like me. I would recommend sticking with USAir. I find that taking connections via CLT gives me the least amount of delays and cancelled flights due to weather. However, when traveling to NYC, I generally take jetBlue because I have much better luck with them than taking USAir out of LGA (LGA can be a nightmare), at least if I actually want to get home at a reasonable time.

With USAir you will have status as a Star Gold on United and Continental as well which will be helpful for your flights to the midwest. You can use your USAir points to book flights for your friends and family.