T-Mobile all the way for me. I currectly have a phone on Verizon and one on Sprint.
Verizon is way too expensive and they like to rape consumers every chance they get. Sprint has unlimited data with "no slow downs" but their network is so damn slow (below 200k consistently) that I don't even want to use their network. Plus, I think I would shoot myself if they "slowed" me down further than 200k. Unlimited, but I don't even want to use it.
T-Mobile is what I am moving to. Great plans, unlimited at $70 without throttle, and they have data that I actually want to use: HSPA+. Even though it is largely not LTE, their HSPA network comes VERY close to LTE speeds. When they get their LTE network out it will be even better. SO not only are they less expensive and without contract, but also just as fast and UNLIMITED.
That's worth it to me. If they cover you where you live, work, and hang out.... I would go TMobile.