Verizon probably is the best, but then it also depends on how much coverage is in your area. Spring might be good in select areas, etc.
Like Sprint sucks in CA for instance.
Good site to see if your area has a lot of dead zones. http://www.deadcellzones.com/
"When nothing seems to help, I go look at a stonecutter hammering away at this rock perhaps 100 times without as much as a crack showing in it. Yet at the 101st blow, it will split in two and I know it was not that blow that did it. But all that had gone before." - Jacob Riis