I have had poor experiences with T-mobile coverage in the Seattle area. They seem to be really spotty up here. For that matter, same with Sprint, they are also quite spotty up here.

Interestingly, I have been super-happy with AT&T coverage in the Seattle area. It's quite good up here, with strong signal in any place I want it. I have seen better signal coverage from AT&T than I have seen from Verizon in the Seattle area.

In order of best to worst coverage for Seattle, my experience has been:
- AT&T
- Verizon
- Sprint
- T-Mobile

... With only AT&T and Verizon being above the bar of what I would consider usable.