I've been with T-Mobile for over 10 years and love them. I've had all carriers but Verizon and don't care for the others. I have a Verizon phone for work and its OK no complaints really. NEVER had any dropped calls on T-Mobile. Customer service is top notch every time. The only people who complain about t-mobile are the kinds of people that will complain about EVERYTHING IMO.
The only thing I can say negatively about T-Mo is that their coverage is limited to major metropolitan areas. I live in a little area in E WA state and there are dead spots. Even so I will STILL stick with T-Mo. My bill can be almost a month late and they won't shut off. Had an issue with an older G2 my g/f uses and they hooked me up with a new SIM card without question to try to solve the problem. I always get through to customer service in under 5 min, usually immediately and the agents are always knowledgeable. I'd highly recommend going with T-Mobile.