Just got into watching this show. So goddamn funny! As said above Murr and Sal are probably the easiest, and in those ways also the funniest. That Joe and Q just usually roll with the scene is great.
Best Punishment that I've seen would be the one with Sal being confronted with all his phobias, the cats, manure, heights all just 'showing up' in the square while he's supposed to be doing a skit.
But damn there are so many more to chose from! Joe as the Genie was great. 'Genie does as you wish.'
I do get squeamish though. I have yet to watch Q's sudden Punishment in the art class all the way through.