Mixto Rio Grande at The Original Ninfa's
I think Robb Walsh was right on the money when he named the fajitas at The Original Ninfa's his second favorite Houston dish.
However, I have never been content to get just the beef fajitas -- or the chicken or a combo of both -- at Ninfa's, whose expansive menu is a nightmare for an indecisive diner like me. My favorite compromise is the Mixto Rio Grande (chicken fajitas, shrimp, and pork carnitas; $21) because then I get to eat three types of animal flesh within a single platter of Mexican food.
The other virtue of the Mixto Rio Grande is that it comes with the same portions of trimmings (pico de gallo, guacamole, beans, rice, grilled onions, and unlimited tortillas) as the regular fajitas, which means you don't have to limit yourself to your "official" filling. I like to combine the fatty carnitas with the leaner seafood so the greasy pork juices coat the crustacean, creating a taste that can only be described as "shrimp bacon." Probably not kosher, but oh so delicious. Especially when anointed with a dollop of sour cream.
For all its offerings, this dish does lack one thing: cheese. Ninfa's regular fajitas do not come with cheese or sour cream (perhaps this is a Mexican versus Tex-Mex cuisine differentiator) and by extension, neither does the Mixto Rio Grande. I recommend you pay the extra buck for a side of cheese or sour cream, unless you're a purist who believes "real" fajitas require no dairy lubrication. If you are, stop reading, because I'm about to recommend something even more vulgar: spring for a queso appetizer and dribble that over your fajitas. You won't be disappointed.