I've been fulltiming for 3 years now and have been all over the country, except for the NE.
You definitely want something that runs on the Verizon system. Most will agree they have the best coverage by far. Probably why they are not the cheapest.
I have had an Iphone since I started out and have used Straight Talk since Day One. Mine runs on the Verizon system (I only wanted one of their phones that would run on the Verizon system). It's worked out great. I can count on 2 fingers the times I haven't had service. Monthly cost is $45 for unlimited talk, text, and sorta data (read how data works with them). No contract.
I have no complaints.
Straight Talk does not allow tethering so if you wanna do that you will need to look elsewhere.
Did I mention it is only $45/month ? On the Verizon system ?