The United States greatest appeal is in its variety - from coast to coast and border to border each region has something unique to offer and you can travel it all without ever having to show your passport.
The U.S. is a great country and it is generally filled with good people - come on over!
I have been lucky, I've seen "some" of this planet ... if I had to select parts of the U.S. to visit I'd say:
1. New England in the Fall. (Mother Nature is still the best artist)
2. California in the winter. (San Fran is the bomb!)
3. Gulf Coast in the Spring. (skip Mardi Gras, go to Jazz Fest)
4. Summer in the Northwest. (Puget Sound is amazing)
Avoid New Jersey!
Nicest "people" on this planet = Swede's, Swiss are a close 2nd (they're a little snobby).
Funnest "people" on this planet = the Aussies, Scottish close 2nd (they get violent)
Dumbest "people" on this planet= Americans, there's no one close to us - sad