Best - National Lampoon's Loaded Weapon 1. There are some great comedies out there, and I'm dying to watch Office Space, but NLLW1 has a soft-spot in my heart.
Worst - Cannot think of the absolute worst off the top of my head, but Napoleon Dynamite is easily the most overrated. I watched that shit expecting some kind of smart comedy, but what I got was a movie that thought it was so clever, yet was so fucking obvious it made me hate my peers for liking it. Never have I felt so alone. I laughed once, and that was when Kip did the leg sweep, the guy jumped over him and slapped him over the head. Ha! That was it.