My favorite, hands down, is Loading Ready Run. While I love pretty much everything the LRR Crew has done, their sketch comedy is my favorite. I've spent hours looking through their archives.
Second position is a constant fight between RMM and ZP. It really depends on what mood I'm in. If I'm feeling pessimistic and cynical, Zero Punctuation is best. If I'm in more of an artsy mood, and want to really think, I watch Rebecca Mayes. But I've laid down my favorite, and I don't feel I should have to choose between these. Meh.