I LOVED the episode with Kelly Preston as Donna. She comes close to being my favorite, but one person wins out. Adam Goldberg was incredible as Jimmy. It was like he was born to play the part with his tattoos and his similarities to Michael. He had great chemistry and intensity, and he just OWNED that part.
My least favorite had to be John Laroquette. While I love him, he just bugged me. I realize his character was meant to be a schmuck, and that he means he was doing his job well... But he still bugged me. Heh.