Three words: hot veal sangwich. Sauce, hot peppers and nothing else. I've tried them all, and San Fran has the best around.
Pre-cooked meat and hot tables make an inferior sandwich. Pickled or oil-preserved hot peppers are just wrong. And a sandwich has to be the right size - big enough to satisfy, but not bigger than your head. This rules out Mustachio, California and all the others.
San Fran's lightly-breaded veal is fried to order, topped with a delicate tomato sauce and roasted hot peppers, and not so big that you're stuffing yourself at the end. Simple and perfect.
Dec. 1/ 12 Update: I visited for the first time in a few weeks. San Fran is under new management, and they redecorated, adding more counter space for diners. The sandwich was as good as ever, though.