Yeah. Try leaving your area or getting to the outskirts of it. 2G galore!
T-Mo is only good at marketing gimmicks (Uncarrier) and lying to the public ("Nationwide 4G")
They might out-perform AT&T/VZW if you purposely cherry-pick spots where TMo actually has working service, but if you actually factor in overall data speeds and coverage, they're not even on the stratosphere. T-Mobile's entire 2G network is about the size of AT&T/VZW's LTE network.
I was using my Verizon iPhone today in a little, rural, middle of nowhere town... called Downtown Los Angeles and got a fantastic 2mb/s download speed outside and zero data inside a building while having a LTE connection. Last week at the Hollywood Bowl I couldn't get any data on my Verizon iPhone but the T-mobile phone got 20mb/s download, and we're talking right in the middle of one of the biggest cities in the US. It seems Verizon may have the edge in the boondocks that I rarely travel to but, perhaps, their city connections are congested or overtaxed because the data has not been great in our experience.
My wife and I travel a fair amount and in just the past 2-3 months have been in LA, San Diego, Seattle, Boston, DC, NY, San Francisco, Santa Barbara and a number of places between and while we've always had 'LTE' data, we often don't get 'LTE' speeds and get maybe 2-3 mb/s download speeds. Verizon may have the largest 'LTE' network but if you're only getting a few mb/s in most major cities then it's not really 'LTE' is it.