That's solely a data comparison, and yes at&t has made strides in the largest markets (there's a map for that). As for nationwide coverage, there's no comparison - they get killed. The real killer here of course is that they're phone calls are handled of their earlier generation network, which clearly can't handle the rise in subscribers as is evident by the high number of dropped calls.
That being said, I always tell people to go with which ever provider has the best coverage at your home and your place of work. For me that's Sprint as evidenced by the reliability numbers - I've never lost a call on Sprint in San Francsico in the 7 years I've been here. I dare any at&t customer to claim the same. I'll sacrifice 150kbps for that kind of reliability, especially with WiMax around the corner. Right? It's still coming soon, right? Eee ghads.