Sprint lies about their coverage I think. They advertise full wimax coverage in my city, but I almost NEVER could get a wimax signal. And the 3G averaged like 200 to 600kbps tops. I never saw 1mbps. People tell me "oh salt lake city isn't a big enough city, they're not going to devote the kind of resources there that they would in a REAL city". Well then they shouldn't advertise it as such. T-Mobile has no problem delivering the promised coverage here. I get 4G everywhere I go, even inside of big buildings.
Maybe they all stretch the truth about their coverage, all I know is in my area both companies advertise good coverage but only T-Mobile delivers. I know att has way more coverage than T-Mobile and I would use them, but since they're more expensive and T-Mobile is great where I live, I'm with T-Mobile.