I personally thought 40 Year Old Virgin was the weakest of the three.
FWIW, though I enjoyed a lot of the movie, the McLovin gag was by the funniest thing in there. Followed by all the scenes with the cops.
Actually, I thought the scenes with the cops were the weakest in the film.
I would second that.
I think I had a great time with Super Bad because I went to movie not expecting it to have the same payoffs as those movies. Instead I expected something on the level of Porky's or American Pie, so I was happy with the results.
I had a similar reaction. Just before seeing Superbad, I talked with a friend who gave me all the reasons why he wasn't going to bother seeing it (and he was a fan of Knocked Up)---consequently, I went in expecting it to be rather weak, so I had a great time. The magic of lowered expectations.