I think I've listened most to the Turtles II episode because Adam Pally just kills it. My favorite moments don't tend to involve a guest, but between his bad father anecdotes and attacking the crowd (honestly, a reason I prefer the live episodes is the audience interaction), it's absolutely my favorite episode.
I also loved Cameron Esposito on Can't Stop the Music. I couldn't stop laughing through the first thirty minutes of the episode.