Different strokes for different folks.
I use cricket (cheaper than both Verizon and att). Only had issues traveling on 90 from MN to WA. I think att has same issues (they own cricket). My brother switched to Verizon once. When we were teaming (4 years ago)he was more often out of coverage then I was in lower states. He switched to cricket then.
I agree with Doealex, if you're switching then go with Cricket. Most of the drivers I work with have Verizon (we get a discount with them) but 1 switched over to Cricket and he pays a lot less. According to him, the coverage may be a little different but not enough to account for the price difference.