Man this is hard. Part of me wants to say Patchy, but there have been so many little gags and stuff that involved live-action and I loved those too. I think I'll go with the Krabby Patty from the KKTV just because that's my favorite episode haha
My favorite is patchy, mostly because of the "when worlds collide" song, and the christmas special. However, the lab joke from "Plankton!" was a close second, because I still laugh at that to this day.