I like the cabeza at Taqueria Sinaloa (the truck at the back of the lot) best. I've found lengua to be fairly good most anywhere that offers it. Both these are quite good at Taqueria Vallarta if you're looking for San Francisco specifically, though Yelp is showing it as closed down (possibly by the Department of Health).
3033 24th St, San Francisco, CA 94110
2138 International Blvd, Oakland, CA 94606