Giving it to Magneto. Luffy's fast and strong enough to One hit KO Erik, but in a junkyard? Lots of sharp, metal objects all around. Until Luffy shows better ability with his foresight haki, I'm going to say Luffy gets impaled before he can land a hit.
But only barely. As in, Magneto's life flashes before his eyes before he realizes Luffy's dying.