Never had any problem with T-Mobile. Got a family plan $119/month (I think, or maybe its $109) for 4 lines, 500 minutes, and 2 lines have unlimited internet (using G1s). We don't really care too much about the minutes, so 500 is more than enough.
I have Verizon (6 years now) and AT&T for business (8 years now). I prefer the Verizon for coverage & billing but I have the right plan and yes that matters 100%. Family plan (2,400 minute plan/unlimited text, etc.) with 6 phones and under $250 a month.
I prefer AT&T simply because of the I-Phone and other phone models but haven't tried out the Droids yet so that may change to Verizon soon.