I've lived in Salt Lake City for 9 years and have tried dozens of "the best" Mexican restaurants in the SLC area, as well as countless taco trucks/trailers. I can honestly say that I have yet to find an asada taco in SLC that I enjoy more than the ones at El Herradero in Pocatello. Their salsa verde is great, beans are good, and I'm addicted to their pickled carrots and jalapenos; even those are hard to beat in SLC. Somehow, even their bean and cheese burritos are great; something that normally tastes bland and dry to me, but not here. It's definitely a hole-in-the-wall, but the food is good and the prices are very reasonable. A frequent stop when we're in town.

Update 4 years later:

We've since moved back to Pocatello and have been going to this El Herradero almost weekly for the last 2 years. I've never been a "regular" somewhere, but this would be the only place I'd ever consider myself a regular; they know us when we walk in. In the last 4 years the food has always been fantastic, and the service has always been excellent and very friendly. We have eaten here well over 100 times and have never had one bad meal.

Just note that authentic Mexican service is culturally different than what many might be used to. Here, you often seat yourself, and when you're ready to pay, they don't tend to bring you a check. When you're done eating, simply walk up to the register and they'll take care of you. It's a system that works well, but it's worth noting since it's a little unconventional for what many might be used to. Don't mistake the different approach as poor service; it's not, it's just different.