Answering your question would be easier if we knew where you were located state wise. The reason I say this is that the J.D Power rankings leave out some carriers. For example, here in Oklahoma, US Cellular has the best regional coverage of any of the national carriers, yet the don't appear in the rankings.

My advice, look at coverage areas for the places you are going to be..who cares if they have excellent coast to coast coverage if you can't get a single unless you are within a mile of a major highway. <img src="/images/graemlins/smile.gif" alt="" />