My favorite real Mexican food would have to be Chipotle. It's great food with spice and your choice of seasonings. They make the food right in front of you too. The only problem with it though is that it's expensive for an everyday thing.
I am a huge advocate of Del Taco. Unfortunately they are located more in the Northern United States. It is a delicious treat that has always been inexpensive for someone on a budget. Tacos from Del Taco hit the spot every time.
My favorite Mexican food chain is Taco Bell. I have been eating at Taco Bell for years, although I don't really diverge from my typical order all that much. I stick to eating basic hard-shell tacos. I had a steak taco once -- they were out of ground beef.