For amazing Mexican food and even better margarita, I choose Frontera Grill! This is by far my personal favorite for Mexican food in Chicago.
Celebrity chef Rick Bayless defines authentic regional Mexican cuisine for north-of-the-border diners at Frontera and Topolobampo, where the latter provides fine dining and the former offers a rustic take. Topolobampo accepts reservations but I never mind waiting for a table at Frontera while enjoying a margarita.
Click here to check out their website to learn more about this great dinig choice.