I've had Sprint for a very long time. The data sucks usually. Slow or not usable at all except in large cities where I don't need it so much anyway. I'm in Columbia, South Carolina, this week, and the data disappears entirely during morning and afternoon rush hour. The good thing about Sprint is that it's available in many rural areas of the Carolinas where I frequently travel.
T-Mobile has rolled out attractively priced no contract plans. I've always thought of T-Mobile as a city cellular service, not too suitable for rural travel.
Sprint = 3 lines, data on all, mobile hotspot on one, about $180 monthly plus taxes and fees.
T-Mobile = 3 lines, data on all, mobile hotspot on all, about $120 monthly plus taxes and fees.
So, keep the more expensive Sprint that has signals in the boonies but sucky, nearly useless data? Or try the cheaper, no-contract T-Mobile that might not be suitable at all outside of cities.
I'd have to lay out some bucks for the devices to try the T-Mobile. You don't get a contract price subsidy. There would be some initial financial pain just to see if T-Mobile works where I travel.
Tentative plan: get the LG Nexus 4's from Google directly. They are cheaper than T-Mobile sells them for. Use them on T-Mobile under the "bring your own device" provision.
Second plan: Get some HTC Ones, continue with Sprint, and hope the data works one day.