What is the best FF program if one is based in Boston? I think I've narrowed it down to American (probably the largest carrier in Boston) or USAir (has BOS<->LGA shuttle, earn miles on United & America West). Which airline is it easier to earn status, which airline is better for receiving upgrades, and which has more seats available for frequent flyer travel?

Most of my travel will likely be to Chicago, New York, and San Francisco.

Thanks for the help.