If you're looking for high-speed data and the coverage in your area is as good or better than why not. They have some pretty good plans right now maybe not as many minutes as T-Mobile but then again nobody comes close but you will get some cool features. I just switched from T-Mobile to Verizon because of the high-speed data and V-Cast.

i think it depends why you want to go to Sprint...

if you are looking for data and pretty good plans then i would go to Sprint but if you want cheap rate plans and nothing else, stick with tmobile.