Washington D.C.: D.C. easily best for views, The place is amazing and beautiful, Monuments everywhere and an extremely interesting place for american history and sightseeing.
Dallas: I've only ever been once and thats because we were driving by it and I wanted a picture of the Grassy Knoll

But I hear its got many sights and beautiful weather.
L.A.: Can't say much more, Crime is horrible in the slums of town and in the high life of town its amazing, If you go then you have to see a sports game there.
San Fran: Very interesting place, Beautiful scenery and unique streets.
New York: Busy, Loud, Polluted but amazing, Dont forget the Nintendo World Store, Its great

Miami: Beautoful Scenery, Gotta love the palm trees and strolls down the sidewalk.
Hawaii: No matter what Island or City you go its amazing for relaxing and breathing in some fresh air. Surfings also Amazing there!