Zoolander might be my favorite performance of his. He's missing from the middle section of the film but he absolutely steals every scene he's in in my opinion. Just seems like the perfect use of his comedic talents and style and such a funny villain creation from Stiller and co.
Best movie? I'm partial to Anchorman and Elf. Though I think Anchorman is a bit of a niche comedy movie that sort of became bigger than one might expect because of the cast. I think Old School probably has slightly more replay value. Vaughan adds immensely to Old School.
One thing I will say, too, is that I found Step Brothers to be funny and I completely got why it was a big hit but it never really resonated with me the way it did with some. That was true across several watches. Just recently, I watched it again for the first time in years. I think I found it funnier this go around than any previous viewing. I almost had to stifle laughter just cause it was happening even as I anticipated certain gags.
What I appreciated this time around was how difficult it probably was to get through some of those scenes without breaking character. Just so zany and ridiculous, with things that probably were not half as funny on paper as they were in practice. When Jenkins and Steenburgen reveal they are breaking up and Ferrell and Reilly start crying and Reilly is blubbering "I'm gonna throw up...I'm gonna throw up" it's just some of the most ludicrous stuff I've seen even in the "silly comedy" genre.
Not only that, the supporting cast adds immeasurably to that film. Adam Scott and Kathryn Hahn have become very successful since (and rightly so) but them, Jenkins, and Steenburgen are all great in it. Jenkins, particularly, strikes the ideal notes in almost every scene. Steenburgen has the tough task of being more of the straight woman comedic performer but she does that really well. Scott and Hahn cracked me up multiple times.
So I think that one has to be one of the best Ferrell comedies too.