I had T-Mobile for a while, but there is no data plan with it, texts took several days to get to people, but voice worked. They were nice about cancelling my contract.
We have two providers in town, Viaero and Verizon. The Verizon pay-as-you-go plan was $10 more expensive a month and they wouldn't let me use my unlocked phone on their system. I don't know why, but I just couldn't be bothered arguing with them. Drove across town and got Viaero. The only down side is if I'm out of the county, I can't get an internet connection.