I don't necessarily have a favourite Mexican, Tex-Mex, or Southwestern restaurant. And I know that that is a really wide variety of foods, flavours, and cuisines, though the lines do often blur.
So, let me write about some restaurants I've liked in various places.
(Note: we didn't have any good Mexican in Miami). In Shawnee the old standard places that folk had gone to for years and years were pretty bad. While I was living there a handful of Mexican places came and went, and some of them were really good. The one that came and stayed and that I enjoyed going to often and that eventually had multiple locations was Abuelita's. This is not fancy, it is typical Tex-Mex greasy and drenched in cheese. And really enjoyable to eat. Especially with the complimentary chips and salsa, tortillas, the little pickled veggies to put in the tortillas, and a sopapilla at the end of the meal.
Nearby in Seminole, OK was Polo's, though it is now closed I understand (there is still a location in Ada, OK). Polo's made the best fajitas I've ever had. A couple of years ago I took a group of friends from OKC all the way to Polo's to have the fajitas. They were that good. Also enjoyed the queso. Polo's was located in the old train depot downtown, so the location was even a little fun, though the bathrooms were odd -- sliding doors.
Stillwater has two very similar Mexican places that are much like Abuelito's -- greasy, cheese-drenched. The salsa and queso blanco in both are good. These places are El Vaquero and El Tapatio.
Dallas, of course, is filled with Mexican places. I never liked the old traditional El Fenix. And Mi Concina, also a standard, was good, but not memorable (though I did like the mojitos).
The best chile relleno I've ever had is from Matt's in Lakewood. I enjoy Blue Mesa and its contemporary southwestern flavours. The restaurants have great atmosphere, and I recommend the Painted Desert Soup (a combination of corn chowder and black bean soup), the sweet potato chips, and the jalapeno relish. Chuy's, on McKinney, I ate at all the time. I like their use of green chile's from New Mexican cuisine.
The Mexican we ate most often at Royal Lane was Cantina Laredo, because it was close to us. Mostly we drank beer there and ate their excellent chips and two different salsas. It was also while living in Dallas that Chipotle became my favourite fast food restaurant.
Oklahoma City, OK
My favourites are those I listed in the last post, the one about tacos. For Mexican when going out to eat with friends, I like La Luna (or for catching a quick lunch meeting). I also really enjoyed Las Palomas, particularly the way they served a Dos Equis in a nice big, chilled glass, with salt and lime. I was never a huge Ted's fan, thinking it was not as good as its reputation and too expensive for what you got, though the tortillas were good.
Santa Fe, NM Area
I love New Mexican cuisine, particularly the green chiles. There are SO many great restaurants in Santa Fe and the surrounding area, but my favourite is Rancho de Chimayo, partly because you have to drive out to it and go through these great villages and enjoy the sight-seeing. But it isn't just that, or the setting, it is great, great food.
We haven't found any great Mexican, Tex-Mex, or New Mexican in Omaha, but Stokes has a nice Southwestern menu.