I'm leaving Sprint to try out the Nexus 4 and T-Mobile. Allegedly, I should get around 10mbps down in my area, which of course is worlds better than the 100kbps or so I get from Sprint 3G. If I don't, however, I'll be a bit torn, because I really don't want a contract but I also have my wife and son who need good service. Verizon is expensive, but bad coverage has a cost of its own. Probably, I'll give the Nexus 4 and T-Mobile a good workout on a prepaid plan (and with Discover I have 90 days to return the Nexus 4), and if it works I'll get one for them and we'll all go prepaid.
Then, in a few years, hopefully the networks will shake out a bit and we'll see what's possible. I really do think, though, that signing a 2-year contract with ANYONE today is a losing proposition, given that there are currently so many moving parts.