We have had both.
Verizon has the better phones and get the newer styles before USC.
When using USC roaming on a Verizon tower, your data gets "Throttled" and you may not be able to make a call. For example...In south Florida there are no USC towers and you are only roaming. I have been within 100 yards of an active tower with USC , with full bars and unable to make a call. The excuse is that USC doesn't want to "rent" service from other carriers.
My USC phone is a work phone and if it was coming out of my pocket...I would be going Verizon.