You are asking the wrong people. Ask your neighbors: the people who live next door, work colleagues, fellow classmates, etc.
If you have a friend who is a T-Mobile subscriber, invite them over to your house. During the course of the visit, ask them how their cellular reception is in your house. That is one piece of the puzzle answered right there.
I live in Silicon Valley. T-Mobile's coverage -- even in densely populated areas -- can be rather spotty and often I find myself on 2G EDGE data. There's really no rhyme or reason to it, and coverage maps aren't accurate enough to show much detail.
T-Mobile's coverage is definitely weaker than Verizon and AT&T in sparsely populated areas. T-Mobile simply has fewer cellular towers.
When my iDevices do connect to T-Mobile's nascent LTE network, the speed is pretty good. Due to a lack of spectrum allocation, T-Mobile was late to the LTE party, but they did acquire some frequencies and finally started building out LTE with newer equipment than what Verizon and AT&T had installed, thus T-Mobile often has really excellent speed.
NOTEIf you work at medium sized corporation or attend a college, you may wish to contact the IT department. They would definitely know which carrier has the best overall performance in the local area, after all, they're the ones supporting huge groups of people.
I would not use a smattering of anecdotes from an anonymous tech bboard like MacRumors to select a mobile network operator.
Despite all of its shortcomings, I am using T-Mobile USA, even if AT&T has better reception. The key factors in my decision is that I have reliable WiFi at home and at work; cellular reception is very weak inside my condo, but good enough for incoming voice calls. I use Google Voice VoIP for outgoing calls over WiFi.
I am okay with getting EDGE connectivity in places where I infrequently find myself because I'm saving a pile of money with T-Mobile. I wish my phone was connecting to AT&T cellular towers, not T-Mobile's but AT&T (and its MVNOs) do not offer the same prepaid plan that I'm currently getting from T-Mobile.