TMobile really does have 3G in something like 240 cities... I know my city wasn't turned on until Late December. But many places have 3G now. And they are supposedly updating to 7.2Mb and then soon HSDPA+ (21Mb) which I think would then make their limited coverage the best. However, their rollout was amazingly slow and I was about ready to give up on them. And more than that, supposedly they have already turned on the 7.2 EVERYWHERE, but it definitely is not turned on here. So I see 5-700kb instead of 4-5000kb. Which is pretty pitiful. But the Android Nexus One is freakin' incredible -- I'm not having the 3G problem that has been reported elsewhere, its just slow here just like all the other 3G phones are that I tested.
Verizon was awful, Spring was Awful, AT&T was fine I guess, but I wasn't there long, I left because I couldn't get any coverage at work. T-mobile has been great (comparatively) as a company but their coverage has been meh so far. I'm still hoping its going to pull through this year and then they really would be the best.