Isn't that sort of like asking for a good American food restaurant. I have lived in the Southwest and visited all the border states, but the best Mexican food I have ever had outside of Mexico was in a little town in Up-State New York. I like some others have said like the "New Mexico" style. Here in Salt Lake I can think of at least five different styles unique to different parts of Mexico. Some good to me, others not so, but very popular with their clientele.
Find your own favorite style by visiting lots of places and learn where the culture influences the food. As it turns out, my favorite place was owned by a woman born in Caliente, Mexico, but grew up in Belen, New Mexico. Only place I ever tried everything on the menu.