I've had many colleagues with Sprint and they have told me that their phones did not work in many places, while my Verizon phone will work almost anywhere. Some places have good Sprint coverage, but often the coverage fails off the major highways.

This is a result of Sprint's go it alone approach.

With AT&T, they have partnered with many local providers so you will probably have coverage in more places. Certain places will be very poor with AT&T but in general it will cover more places.

Verizon has the largest network and is the best in my experience although the most expensive also. And there are places with poor Verizon coverage that have great coverage with another carrier.

If coverage is an issue, you may want two providers and carry two cellphones. I carry T-Mobile and Verizon and often if one doesn't work, the other does.