Mmmm! Fried bread porn!
Tomasita's is not my favorite place in SF, but their sopas are good.
El Patio still wins this hands-down, although the sopapillas at Cocina Azul are also very tasty.
Stufy's, of course! 14 different types of stuffed sopapilla's - http://www.stufys.com/The_Menu.html
(I keep on meaning to try the new one on Juan Tabo....)