Neither carrier has great service in Utah, if you look at the coverage maps, they're about equal. With AT&T you'll get faster data speed, however, as a whole, Verizon has better coverage in the US. You can click on the coverage maps to make them larger.
Also, it's to my understanding that carriers will let you "try out" their service and if you aren't satisfied in the first 2 weeks or something, you can cancel it.
I believe Verizon gives you 14 days to try out a smartphone. If you don't like their service, you return the discounted phone you purchased and pay for what services you used.