The only company I can say I had satisfying service with was through T-mobile. We have to deal with their weird mall shacks, but at least you get in and out quick. With verizon, they give you good service, but absolutely horrendous customer service, whether it be in store or through the phone. You better hope nothing goes wrong with your phone like it did with ours! I wouldn't mind going back to Tmobile, but they don't really have anything special(in terms of plans) for me to switch. If I were to switch to anyone from ATT, it would probably be Sprint...when the iphone comes out.
As for the Tmobile and iphone comment, there are a lot of people who come in with unlocked iphones on Tmobile plans. A LOT!