I can only speak to my personal experience in OK - and from the perspective of the engineers who are building the network here. Whether or not what is being said matches up with reality is something we'll have to wait and see. I'm far from a TMO evangelist, but I'm pretty impressed with what they've done in my state in a short amount of time.
For work, I always have a current flagship from each carrier in my desk drawer, and I rotate them out frequently. VZW continues to be the most consistent carrier in my state, with AT&T lagging behind slightly in the more rural areas. T-Mobile has always been the worst outside of the city, but that is changing very quickly. Sprint, on the other hand, is an absolute disaster in the OKC metro. It's no more usable than it was a few years ago, but again, that's just one guy's perspective. I'm all about rooting for the underdog when they deserve it. In my region, Sprint has done tons of modernization but the cell grid is still so sparse. They don't stand a chance in this state unless they start putting up more macros, which doesn't seem like it's in the game plan any time soon (unless I missed something).