I actually have better T-Mobile coverage at my house in the Berkeley hills than I did with Verizon. However in most places the coverage is worse with T-Mobile than ATT or Verizon. In general, around town and on major highways, the service is acceptable to me. There are small gaps in coverage here and there, but I have no problem streaming music or video until I get into the hills.
For riding, the coverage can be a bit lacking, even in the Bay Area; I will have service on ridge-tops, but generally not on hillsides or in ravines (East Bay, Tamarancho, Annnadel).
Overall, the tradeoff is worth it to me. YMMV.