Let's assign a best gag from every episode. We will go one at a time in order. Feel free to dispute anything somebody lists, so long as we do not lose count.
I will begin with Simpsons Roasting on an Open Fire. Simply state the number of the episode (eg 1.) then describe he gag.
1. When Bart imagines Marge's reaction to his tattoo, saying "Oh, Bart, that's so sweet. It's the best present a mother could get, and it makes you look so dangerous."