Your question is more complex than you think. Flyertalk has thousands of posts about ff programs.

Goals also vary. For some, it's upgrades and elite status. For others, it's domestic coach tickets.

See which airline's routes fit you first. Is it UA, AA, NW? How about Midwest Express. That's a nice airline where every seat is an upgrade, though you have to connect in Milwaukee. They only fly to many major East Coast cities, not all (e.g. not to PHL).

I like US Airways and Northwest. These might not fit you, though. US for the tad better service and NW for the awards availablity and easier upgrades.