Hard to say. Sharks really don't kill many people. Weirdos with Mommy issues doe. So I give it to Psycho on the credibility angle. Jaws had a better soundtrack and a better cast when you get down to it.
Psycho is definitely more creepy. I don't think anybody would doubt that. It's hard to beat Jaws in terms of watchability though. And in terms of acting, the trio of Roy Scheider, Robert Shaw, and Richard Dreyfuss all turned in terrific performances.
