General

If you're going to be traveling a lot, don't stick with US Cellular. They only have coverage in about half the states, and beyond that you'd just be roaming and might be charged for it (I don't know how they handle it). For instance, all of Florida is roaming for them. I know this from experience because I checked (living in Florida and all).

Who you choose is up to you, but for extensive traveling, one of the 'big four' would be the best route to go, since they have more national coverage and less roaming. Though I also know AT&T has almost zero coverage in Nebraska, it's all roaming coverage, so you can keep that in mind too. As far as extensive coverage goes, Verizon would probably be the best bet.