A few bad physical locations notwithstanding (and find me a cell network where this isn't the case) I really couldn't complain about Sprint's network coverage too much. It happened to be that my home has some random and shifting dead spots in it, but whatever. Their customer service was itself fine, both in-person and over the phone.
But two things really soured me on Sprint: their high rates for service, and their handling of 4G service.
I've switched to T-Mo, and most of the time use GrooVeIP for VOIP with my Google Voice account. It works reasonably well, and saves me $50/mo in plan price differences. So far that has fully paid for my ETF and my phone itself, so I can't imagine for just that reason alone not having switched.
The other thing, and this is more philosophical in nature, is that I'm done with CDMA because of its vendor lock-in nature. I'm also done with ever being on a contract.
So as far as WiMax is concerned, as I and other have already beaten to death in this thread, there is no longer a point in considering it, any more than there's a point to HD-DVD or Betamax.