Go for the one with the best coverage in the area(s) where you will be.

There is no 100% good cell provider. Each and every provider has pockets of no coverage. Some have stronger coverage in some areas and weaker in others. Some are dominant in certain regions. Some have capacity issues in certain areas where calls can't get through. What one person says here about a cell provider may be true in his/her experience but may not hold true for you.

Best thing to do is ask people in your local area with travel patterns similar to yourself and find out how satisfied they are.

Bottom line: if there were indeed a cell provider whose network were flawless -- no dropped calls, no coverage dead zones, no network busy messages, no problems anywhere -- they'd charge $100/month for a base plan for their service, and tons people would pay it because they're superior. Unfortunately, no such provider exists.