I miss T-Mobile. Magenta or not, for all the years I had T-Mobile (think Powertel > Voicestream > T-Mobile) they were great. The customer service was freaking amazing as well. I left for AT&T over coverage issues after they did not renew their roaming contract with one another. AT&T was so incredibly inept that I left and went back to T-Mobile for a time before finally caving in for Verizon specifically for the GNex. I will say it'd be nice to be back on T-Mo, it's a shame that as soon as you leave any major metro area area around here, you're stuck on Edge. They're awesome in Florida. They're awesome around LA. Travel anywhere remotely rural and you're screwed.
Sprint suffers from the same coverage issues. If AT&T hadn't left such a bad taste in my mouth, I'd give them another shot. It sucks too, because we all know what it's like to tinker with a CDMA phone.