Wow, there's so many to choose from. I guess when I'm in the Bay Area, I like going to El Tonayense, El Taco Zomarano, Santo Coyote, and Nopalito, and I'm always on the look out for new food trucks. There are more upscale restaurants that try to be authentic, like Mamacita and Mocajete Cocina, which I've been to, but they are a bit too much on the haute-cuisine side for my taste (and wallet). When I'm in L.A., I like La Sirena Azul, Taquiera Los Anaya, Casa La Dona, La Noche Buena, and again, I'm always on the look-out for new food trucks. I don't mind going to an eatery with a culinary-school trained chef, but I prefer a family-run restaurant (brick and mortar) or food truck with their own recipes, so "authenticity" defined in terms of a particular culture and ethnicity but also within a particular family.