If you get prepaid from a major carrier, you will have the same coverage as a contract phone with that carrier has.
Verizon does not limit coverage (as an example) based if you are prepaid or not. If a contact phone has coverage, a prepaid one will have coverage standing next to them too.
I've been using prepaid for years, and have never had a coverage problem where somebody else on the same network had coverage and I did not.