I'm a huge Seinfeld fan. A few particular favorites of mine:
Elaine gives Kramer her muffin stumps to get rid of, so he gives it to the homeless
Jerry makes Kramer drop a Junior Mint into that guy at his surgery
George gets an enormous wallet to store all his receipts
Jerry's girlfriend catches him scratching his nose (It wasn't a pick!)
The Soup Nazi episode
Kramer gets Jerry to record a movie at the theater for his bootleger friend
Jerry “agrees” to wear Kramer's girlfriend's pirate shirt
Kramer thinks he sees a “pigman” at the hospital
A mechanic steals George's Twix
They're all hilarious, so it's very hard to choose.