If you're going to use peanut butter...use Crunchy. I find smooth is too easy for the mice to eat without tripping the wire of death. The best bait I've found so far for the old school traps is a bit of Tootsie Roll.
Chew on it for a minute or two to soften it, and apply. It sticks well and the mice love it.
And I put a little peanut butter on the bottom side of the trigger, it's death on those with a light touch.
