I have both AT&T and Verizon. I thought that AT&T was the worst until I got a (company supplied) Verizon and am now convinced that one is as crappy as the other. But lately Verizon has been somewhat worse. Just an observation as a user of both.
iPhone’s weren’t available to the entire state of Montana until a few months ago, because AT&T’s service was sporadic (limited to urban areas). That changed after AT&T bought Alltel’s network infrastructure.