While every episode is a timeless gem of writing, the "Puffy Shirt" episode, contains by far the most intertwined plot, with both numerous things going on and references to other episodes...
hand photo guy: "I hope you have a little more self control" George: "Don't worry, I won a contest."
this episode also contains the funniest exchange of dialog in my opinion, by my favorites, the Costanzas
Estelle: "Georgy, do you want some Jello?" Frank: "Why did ya put the bananas in there?" Estelle: "George LIKES THE BANANAS!" Frank: (screaming)"SO LET HIM HAVE BANANAS ON THE SIDE!!"