There are too many worsts to name, but best, despite my love of classic horror, is Evil Dead II. Its just awesome.
I don't know if it's the best, but my favorite would have to be the 1934 "Black Cat" with Boris and Bela. The plot is creepy and weird even by todays standards. Worst.....anything that involves Michael Bay or Keanu Reeves.
Actually, the original shoot script of the Black Cat was even more perverse. Still, I am always surprised by what they were able to get away with through the use of suggestion.