That's really tough to say for certain, cause it ALWAYS changes for me. Funny movies that have come out recently that I enjoy thoroughly are:
Hotrod-I will NEVER turn down the chance to watch this movie
Hamlet 2- Written by the same woman as Hotrod, I've seen it about 20 times
Stepbrothers- Funnier than Anchorman IMO, if only for John C. Reilly doing his first leading role in a comedy movie. I love that guy. Go Dr. Steve Brule!
You can't realistically list any Monty Python movies as the funniest, cause each is an instant classic. No one movie is better than the others, they're all great, beyond classification.