For me personally, it’s the Season 8 episode “Space Mutiny”, which was also the first MST3K episode that I ever watched.
That bit with Mike bonking his head on one of the many railings Servo placed in the Satellite of Love and tumbling all the way down it while yelling before splashing into water sent me into an absolute laughing fit. I laughed for a good 10 minutes at that, I kept replaying that scene. It was pure comedic gold.
Manos: ✋
Final Sacrifice.
Their bit over the end credits with Tom trying to pitch a Finale Sacrifice series absolutely cracks me up every time.
Tough question! I see people have already mentioned Space Mutiny and Manos. So I’ll go with Werewolf.
They sleep nose to anus, like a coyote.
Space Mutiny is my favorite, but since OP already claimed it (now who will bring toys to the children!?) I’ll go with my close second, Overdrawn at the Memory Bank. It’s such trash and Raul Julia tears up every blessed scene he’s in. He only dabbles in dopples but his love for the cinemas is easy to reciprocate.