Both AT&T and Verizon are planning LTE rollouts on their recently acquired 700MHz blocks within a couple of years. Verizon (in conjunction with Vodaphone) has stated that they plan to start testing LTE this year, in hopes of a 2010 launch. From what I've seen on respective wikipedia pages, LTE looks faster, and I'm not sure how much faith I have in Sprint rolling out WiMax in the near future (as they've been saying that they'll start since mid last year, and we were supposed to have it here in Boston pretty close to now).