I'd say Singletary. He did the least with the most. Erickson was a fall guy and went 7-9 with a mediocre team then 2-14 with a team that even Bill Walsh would only get 4 wins with. Nolan I think at least tried to build a good team but he wouldn't stay out of the offensive play calling. He was the head coach though so its hard to blame him for that.