As far as Pittsburgh goes, Emiliano's is some good Mexican food with great service. Daily food and drink specials are always appetizing as well and the wait is never long.
I've had several items on their menu (nachos, quesadillas, chimichangas, burritos, enchiladas) and I've never been disappointed for lunch or dinner. The service is always prompt, attentive and friendly. I've been seated in the main dining room, at the front bar and upstairs. I haven't yet had an unpleasant experience. It accomodates singles, couples and even larger groups easily. Though when it's crowded it can get loud.
While some might debate here over the authenticity, if the point is to keep me coming back for more, Emiliano's wins.