What is the best city to visit in U.S.A?

I would like to visit America in future and question for me is witch city is best to see.I know that are lots of nice cityes to visit.May focus on America is wide.I mean in America are diffrent places to see like some where are forestes,waterfalles,lakes,sea,cityes full of fun and buildinges to see.I like to visit L.A or some city near by bike parkes.