Taqueria Cancun 2288 Mission St San Francisco, CA (415) 252-9560. It's not an accident that Taqueria Cancun makes some of the best (and cheapest) burritos, tacos, and tortas available anywhere. Co-owners Gerardo Rico and Pedro Grande have been perfecting their craft for over a decade, both as taqueria workers and proprietors, and their passion shines through brilliantly in their work. Nestled behind a tiny storefront in the heart of the Mission district, Taqueria Cancun is one of San Francisco's true burrito landmarks. Complete with a shrine to the Virgen de Guadelupe, multi-colored flags hanging from the ceiling, and scenic murals on the walls, Cancun's interior decor is nothing if not festive. Well-seasoned, tender chicken, infallible al pastor, and succulent carne asada typify the meats available in your bulging tortilla bundle, although beef head, brains, and tongue are available for the more adventurous carnivore. The enormous super burritos at Cancun -- with cheese, sour cream, and fresh avocados in addition to the standard beans, rice, meat, and salsa -- are so good that it's difficult not to finish one. In fact, there isn't a weak spot on the menu at Taqueria Cancun and any ingredient combination will be satisfying; just don't forget to plan on a nap afterwards. All material ©1998 Gibbs Smith, Publisher