I hesitate to firmly rank them because my mood changes day to day, but La Cumbre, La Taqueria, El Castillito (the one on Mission at 17th only, NOT the one they mention near Church and Market ), and El Tonayense, a taco truck that always parked at 14th and Harrison are my favorites. And I'm going to give a shout out to Cactus Taqueria in Berkeley because not only are they good but they are actually still cheap!