There's not a lot to be said about The Contest that hasn't already been said. By saying it is probably the best and funniest episode of a sitcom ever would just be adding to the already blurred cloud of similarly phrased adulation this has already received. But I'll say it anyway.
This is probably the best and funniest episode of a sitcom ever.
I first watched this about six months ago, and I've watched it again about five times since, always using it as the sample episode to try and get friends into Seinfeld.
If I was stuck on a desert island and could only take one episode of a TV show with me (to watch on the islands customary TV/DVD twin set), I would take this. It rises above every other television comedy ever written.