Leatherface on paper sounds scary. But he really wasn't that scary. Though in real life, he would make me poop my pants. Myers was pretty scary in the movies. The music and suspense gives it to him. He also had brute strength and was never really dead. Michael Myers was basically a terminator.
Let her face do what? *rimshot* ........ *crickets* .......
Leatherface is a relentless adrenaline rush of fright. Michael Myers benefits from the atmosphere in which he appeared. If I saw both of them while I'm in a large group of people, I'm naturally going to be more terrified of Leatherface. However, given the right circumstances, Michael's stealthy little "gotcha" appearances can be chilling (looking down a dark hallway, standing outside the window, etc...).
@sheenlantern: Him too. Though he was practically an antihero in that silly film's sequel. :D