I think its a function of where you live and travel destinations. I would study the maps. I have AT&T iPhone 5S and love it. No problems with service or customer service. I either visit AT&T or Apple with technical questions.
When we lived about 2 hours mort of where we are now, we had Verizon. We actually had o go outside our house to make phone calls. But, hat being 5 years ago, coverage changes.
When I moved to Wellington, FL, I asked the local Fire Department which service most members had and that is why I picked AT&T in my area.
Bob & Sue Rowan
2012 Coachmen Mirada 29DS (SOLD)
2015 Keystone Bullet Travel Trailer
2016 F-150 Lariat with Auto Trailer Backup
Dog = Morki (Yorkie-Maltese) - Zoe