In these parts you have two basic options when it comes to fast-food Mexican. Chipotle is a special case and we'll deal with them after we get done trashing the national chains.
Taco Bell: B-minus
This is the McDonald's of Mexican fast food, or would be if they served breakfast and Coke. Most items are fairly bland but can be spiced up with the ubiquitous sauce packets. Prices are also pretty reasonable, which is another reason to compare them to McD's, and most of them seem to be open until all hours, which is another plus. Points off for Pepsi and lack of breakfast items.
Taco John's: C
On the one hand they have Coke product, which is a big plus, but on the other hand instead of a taco you get Potato Oles with your combos, and the POs have only a little less salt than the Dead Sea.
Fresh salsa is available but none of it appeals; the sausage in the breakfast scramble is hot dogs instead of chorizo. Add in the fact that everything costs more than it does at the Casa de Chihuahua, and they lose on several points.
This is a good example of how you can find success by doing one thing well. Chipotle specializes in burritos as thick as the average person's forearm, filled with high-quality meat that actually looks like meat as opposed to the ground-up semi-liquid meatlike product found in most fast-food Mexican joints. Cilantro rice, beans (cooked within an inch of their lives, sadly) and one of four fresh salsas plus cheese, sour cream and lettuce complete the monster. You can get fajita-style veggies instead of the beans, add guacamole for six bits extra, get it in taco shells or a bowl (HERESY!) but that's about all the variation there is in the menu, which allows you the choice of shredded beef, steak, chicken, or pork (all braised with chipotle peppers) as well as plain cheese for the herbivores that walk like men. ^^
All this and beer too, what's not to like? Not much. One of these burritos is pretty filling even for a large guy like me; two of them would probably make somebody's stomach explode. Prices are quite reasonable, too, comparable with the price of a combo at either of the other two chains. This is probably the best idea the folks at McDonald's have had since they invented the Egg McMuffin.