I have 2 phones: An iPhone SE as a personal backup with a Tracfone plan, and a work provided S9 on US Cellular.
In Iowa City the reception on both phones is fantastic. Between Dubuque and Anamosa I get no data coverage on my iPhone SE. ATT sucks in Dubuque/Galena in particular. My SE can literally gain or lose several bars (never mind LTE) depending on where you are. Its a joke. USC on the other hand is pretty good, but USC uses their own special network which makes it a pain to sell phones tied to USC on eBay or whateever.
Anyway if you're around Iowa City/CR than ATT should be pretty damn stable. I'd look elsewhere if you're northwest near Dubuque/Galena etc.