I'm positive Steve Carell has overstayed his comedic welcome and needs to move on to other shit. Playing the idiot in every movie he's now, it's getting tiring. Little Miss Sunshine was a great change for him, and Dan in Real Life wasn't too bad. Carell really needs to start exploring roles.
Adam Sandler I think peaked at Big Daddy/Mr. Deeds, afterwards it was just a steep downhill slope.
Jim Carrey is one of my favorite comedy actors, and he actually pulled off serious roles well. He's the king of physical comedy.
As far as Ben Stiller, I have to say he's only funny when he's playing an extreme. Ever since Meet the Parents he gets typecast as a neurotic normal guy, when instead every role he does should mimick Zoolander or Dodgeball, at least his character in them.
And Will Ferrell...ugh. Anchorman was a peak, and after that, rock bottom for life.