Sprint is pretty good as long as you don't go above Grayling too much. I use it and I travel a lot across the country and unless I'm in the boondocks, I get a decent signal. The plans are good, minute and cost wise. I also get free long distance, since my friends are stretched form Alaska to DC to Louisiana and lots of places in between.
I have 5000 minutes (500peak, 4500 off peak) for $50
http://www.sprintpcs.com