I made the switch from Comcast to T-Mobile about 5 months ago and the internet service itself has been consistently good. Very few drops or spotty connections.
However, the issues around strict NAT Type, inability to set static IP addresses, and the lack of UPnP features creates an environment in which online gaming is so inconsistent I don't know why I even bother trying. You can go back so far in the forums and see people complaining about this and we haven't even got a tiny bit of information in terms of them addressing the issue. On top of that, support seems to have no idea what the actual issue is and they keep giving me the same run around.
Genuinely hope this is actually being worked on, because it certainly seems like it's not.