Currently on Sprint with an Epic 4G and I will be switching back to Verizon immediately, selling my Epic and paying the ETF once this is released. Sprint is actually the more expensive family plan due their lack of flexibility in their plans.
Verizon's reception is actually good at my workplace and they offer 3G at my vacation home in the hills of Tennessee unlike Sprint. I also have much more faith in Verizon to fully expand their LTE network, whereas Clearwire seems to have stalled.
It was really between this and the Bionic, but Sense 2.0 and my previous experience with the Evo 4G won me over. It was just a pleasure to use and HTC's phones have a nice, more heavy duty feel to them, at least compared to my Epic. No locked bootloader is a plus. Last, but not least, like some I may get the Xoom and that'll give me my dual core fix for now.
It was a short run with Sprint, but I just need that reliablity of the Verizon network again. Sprint's customer service was pretty good though, I'll give'em that.
Get here fast Thunderbolt, I'm gettin' antsy.