One way to check out which carrier has the best service in your area is the FCC cell coverage map. So far, it's been very accurate for me.
For Verizon LTE Voice, I'm getting 1 bar of service on the camera but it's still transmitting. Verizon LTE Data should have even better connection. May be similar with AT&T.
https://www.fcc.gov/BroadbandData/MobileMaps/mobile-map