@ljs @cwayne @sven
In 'n out is excellent. So is Popeye's for fried chicken (far better than the older more famous KFC, Kentucky Fried Chicken)
Arby's certainly is popular but I personally detest it. Same goes for Subway sandwich chain (try any other available sandwich place instead).
Those are the only two fast food chains I outright hate to the point that I don't understand why anyone ever eats there; everything else is more a matter of taste.
But apparently that's just me, so maybe you'll be lucky and enjoy Arby's. Their menu certainly *sounds* appealing.
But keep an eye peeled. The U.S. tends to have far more variety (mexican, chinese, vietnamese etc) than you'll see in most of the world (with some exceptions in parts of London, Berlin, Tokyo etc), because of the influence of immigration plus not really having evolved much of a native cuisine outside of expensive high cuisine and outside of traditional cheap diners, which tend to be American food).
But I'm not sure about Salt Lake City; I haven't been there since I was about 5, and it has a reputation for being non-diverse.