Pappasitos should only serve fajitas--and only chicken fajitas at that. Great homemade tortillas, tremendous tender chicken, the butter sauce to put them over the top; and you can even get them with skin or without. I'm not a big fan of the warm salsa--if you could sneak in El Sol y La Luna's salsa (or any other suitable replacement) it would be fajita heaven.
If you want great enchiladas or breakfast then go to one of Austin's many unique and authentic places, but if you want awesome chicken fajitas then Pappasitos is it IMO.