I switched a couple months ago, and initially was very happy with it. But recently, I've decided to move back to Cricket, because Mint's network slows to a crawl during the evening when I am most likely to be using the phone: so much so that apps and websites frequently time-out, and my traffic apps don't work on the drive home. From what I understand, network congestion can vary greatly by area, so hopefully it's better in your area than in my mid-sized midwestern city.
Wireless service is very subjective: it can vary so much based on location and usage. Hopefully it really works out for you!