I don't know about Sprint or T-Mobile, but we had a couple bad experiences with Verizon. A customer service rep changed the minutes of our family share plan without permission and we got popped with a 500 bill. When we tied to change it back, we got charged 65 dollars a phone. I now use AT&T prepaid monthly $50 dollar unlimited plan and can never get a human on the phone.
I got my son Boost mobile prepaid and am pleased with that. I can easily get courteous people on the phone.My son gets service everywhere. Our bill is down to 35 dollars a month for unlimited everything.