My long standing fav is Red A Bakery on Clement in the Inner Richmond.
A while back they converted into a Hawaiian BBQ place, but seem to sell the same pork buns and coconut buns they had when I lived nearby.
My thought is that the bun should have a lot of shredded pork and good sauce, but that the sauce should not be too sweet, which is common.
Will travel for a good one. Whose are the best?