Though San Francisco is a mecca for Mexican food, and the Mission is the city's Latin heartbeat, there are very few sit-down Mexican restaurants in the 'hood (you'll mostly find counter-service taquerias).  That may be the reason there's always a line outside of this long-time local's favorite, though the dirt-cheap pitchers of frozen margaritas are certainly popular. Patrons aren't coming for the decor, certainly, which is one step above a diner (the original art for sale on the walls gives it a touch of class). As for the food, it's solid: tasty and very cheesy enchiladas, a posole stew that must come from someone's abuelita's personal recipe and warm, freshly made chips with salsa. For a hearty, inexpensive and authentic Mexican meal in San Francisco, it's hard to do better.