There are only really two sets of towers: ATT or Verizon. So, look at what towers the “service” are using and whether that works in your target areas or not. Then, figure out how much data you need. Data seems to be the biggest difference. If you only need it for a trip from time to time, you could buy a prepaid phone/plan and swap sims at will. I did that this weekend because I knew there was zero ATT coverage where I was going, but decent Verizon coverage. Not all phones can work with ATT and Verizon. I bought mine just in case I wanted to do this swap. Worked well for the last few days. Yes, I had a different number for the Verizon sim.
There are now cable companies that give good combo deals for phones if you have cable, for instance. Again, look at what towers they are using. A cheap phone won’t do you any good if you never have a signal.
On final thought, really,
not all phones are created equal. Some support more channels and if they do, they generally have better coverage from the same service’s towers. Newer channels are being added to newer towers. If you have an older phone, you may not be gaining the benefit of that “increased” coverage.