The Evo 4g is very nice, if you don't mind typing without a physical keyboard. If you like having a slide-out keyboard, and like Sprint, I'd suggest the Epic 4G.
just so folks dont' have to search, the Epic 4G has a faster processor, newer graphics chip, newer screen technology, and a physical keyboard... The only place it really loses is that the Evo's screen is larger (by .3" i think).