This really is the perfect first ask to get, but I'm going to ruin it by listing my top 3, because I can't choose just one.

Mysterion Rises: I love superhero stuff. I love Kenny. Doesn't get much better than that. The superhero trilogy in general was great, but there's still a bunch of loose ends and things that were left unanswered, and I actually have a big AU brewing in my head that ties together a bunch of Lovecraftian entities into Kenny lore... that's a topic for another time though.
Christian Rock Hard: Tolkien and Cartman's interactions are so funny, and Butters farting on Cartman and flipping him off at the end is just chefs kiss.
AWESOM-O: Butters being an adorable naive idiot for an entire episode is just classic South Park, but he does get a win at the end, which bumps it above the rest of Butters being adorable and naive.