Sausage, green, potatoes, cheese... I don't know why exactly it's better than all the others, but it definitely is. The chile isn't too spicy, the sausage isn't too greasy or overcooked, the tortilla has just the right amount of softness... man I want one right now. Wife loves bacon green, and I've tried chorizo red and ham green too. I've had BBs at maybe a dozen places in SF, ranging from the $3 burritos at Blake's and the $12 burritos at some of the cafes - smothered, handheld, sit-down, to go, green, red, xmas, it doesn't matter. Best BB in SF.
... In case you can't tell, I never order anything else from there, so I can't comment on the other food. I think I've had their enchiladas at a friends house, and they were tasty, but that's it.