AT&T has the best 3G if you have good coverage. I just read this engadet report:
http://www.engadget.com/2009/05/26/e...er-in-america/
Tha thas AT&T's 3G as the best overall in their multi city test. I can also vouch that it is the best here in my neck of the woods too. If it was as cheap as Sprint, I would still be with them.
Verizon is basically the same as Sprint but way more expensive and with better customer service.