Had T-Mobile for years with no issues. Was cool cause cheaper than others and service was good. They just changed their terms on data usage so you can barely use it while roaming and then it shuts off until the next month so I switched to Verizon as I gotta have internet while roaming/traveling. Verizon costs more than t-mobile but I travel too much to not have internet.
http://news.cnet.com/8301-1035_3-573...oaming-limits/
Currently have iPhone4s & Blackberry on Verizon and 1 Android phone still on T-Mobile
If you travel a lot and use data think you need to be looking at Verizon or ATT