Just be aware that while Sprint is getting better everywhere historically Sprint tends to dominate in rural areas.My brother and I were in an ATT store. (I have ATT and he just recently switched to sprint) we were talking about this in front of the ATT rep. The ATT rep said "there isn't lte on sprint" my bro whipped out his iPhone 6 and had lte coverage as well as 4 bars to my 3. Shut the rep up quickly. I need to get him to run the speed tests just to see truly how fast it is in comparison.
I believe I mentioned that before but it bears repeating. T-Mobile on the other hand, tends to dominate in the urban market and has really been pushing to modernize their network there and thus gain market share.
As scaredpoet suggests, you might wish to take a T-Mobile test drive if you live in an urban market. Just be aware that T-Mobile will place a credit hold on any card or account you use until the test drive phone is returned.