I'd definitely go with the 8700! While I vastly prefer T-Mo service (and prices, last time I checked) to Cingular, I have to admit that I think the 8700c is nicer than the 8700g. That's purely cosmetic though, and as such, is not a very good reason to make the choice.
As much as I love the 8700, I would not go with T-Mobile unless I could verify that I could get the coverage I need. Otherwise like the others have stated the 7130 appears to just be smaller form factor of the 8700 without a QWERTY keyboard.
If TMO or VZW appeals more to you, then buy based on carrier. If you'd rather havea smaller phone, get the 7130. If you'd rather have a QWERTY keyboard, get the 8700g.
8700 and 7130 are virtually the same phone. 8700 has a bit larger screen and qwerty keyboard, 7130 has a better phone shape. Personally, I prefer the suretype to qwerty, but i have friends who are just the opposite. Try them both and pick the one you like. I don't think you'll be disappointed with either choice. Good luck!
I just got my 7105t but its slow as hell. I was thinking about switching to the 8700g with tmobile or should i go to verizon and get the 7130e. which one is better. Please help
You also need to consider the service and where you plan to use it. My guess is, Verizon has better coverage. T-Mo is most likely cheaper. If you plan to travel outside the US (other than the Far East) T-Mo or Cingular would be better.