There are three technologies that the carriers are calling "4G", and they're fairly different. Forgive the acronym-itis here, but this is going somewhere.
HSPA+ wasn't 4G anything until fairly recently, when T-Mobile decided that they had better call it that in order to not appear to have a 4G solution for folks. This is really an extension of the last gen of technology, and it's fine, but probably not what you're looking for.
WiMAX is the technology that Clear and Sprint use, and it's the odd man out as far as what everybody else in basically the world decided. Clear has really oversold their bandwidth and can't keep their network working, and Sprint is already making noises about abandoning WiMAX and going to a different technology. At this point, WiMAX is starting to look like a technological cul-de-sac. Given their service problems on top of that, and anything from those guys (particularly in the Seattle area) looks like a loser.
That leaves Verizon's LTE network. They've only recently started rolling it out, but it's blazing fast for now and LTE is the tech that more or less everybody settled on (except Sprint), so there's not really any concern about it being the right path. Since right now, their prices are competitive, they're a clear winner.