Burrito Eater, a site billed as “San Francisco's top resource for taquerias and mustaches,” hosts a biannual life threatening exercise called Slab Scrum to determine the city's best burrito. (If they did it every year, the site owner's life expectancy would probably be sadly short.)
This is always a fascinating competition to watch unfold on the site because the Burrito Eater is not biased toward the Mission more than it has to be. While it's the acknowledged ground zero for the burrito, other neighborhoods have managed to fare very well in this food-focused process. Just ask the Fulton Street location of Papalote, winner of the the 2010 title.