Carolinas is an institution in Phoenix, hands down. They make their own tortillas in the restaurant, and they are the best you'll ever have! They literally melt in your mouth, also try the butter tortilla, its the best carb overload you'll ever have.
A few other good things to try here:
Machaca burrito or taco
Bean and cheese burritos
Tostadas!
Red and green chile
In all honesty anything you get here will be good. Don't be turned off by the area, its not that bad at all. The worst parts of town are over west of the 17 and further west of central, like way further west! Minus one star because their hours are fucking terrible. They close at 7 or 8, and they're not open on Sundays. This makes it a pain in the ass to get to on a weekday, since I'm coming from Tempe.