I'm on T-Mobile in Philly and I must say they are certainly improving. They still are not as good as ATT (had in the past) and Verizon (I also have a Verizon account), BUT they are getting there. In or around big cities on T-Mobile you are fine, often you will get 4G LTE or if not at least H+, the problem comes in when you get outside of the cities you are lucky to get EDGE and often you get nothing. Verizon I get LTE almost everywhere and where I don't I at least get something. I'll look at the T-Mobile phone at it will be no signal and then look at the Verizon phone and sure enough 1 or 2 bars and enough of a signal for a call!
BUT all throughout Philly and surroundings I am fine with both phones. I'm talking about out camping in the poconos, or upstate New York, or back woods Virginia or something.