I've switched from sprint to T-mobile last November and couldn't be happier. My speeds are faster than anything I've ever seen on sprint, I've seen anywhere from 1.8mb to 7mb. Also if you read this report below you'll see that T-mobile is faster than anything sprint has to offer. They also are even faster than Verizon LTE in some areas:
Fastest Mobile Networks 2012 | PCMag.com