Agreed, this, +1, QFT, what have you.
I think a better discussion would be in terms of best SNL sketch rather than episode. Whenever I've talked about SNL with my work colleagues, we've always referred to individual sketches or "sketch series" (e.g. Mister Robinson's Neighborhood, Church Chat, Samurai, Celebrity Jeopardy).
EDIT: Oh, wait, I didn't actually name any fave sketches, did I?
Well, the original cast (Murray/Aykroyd/Belushi) was a little before my time. More of my faves came afterward.
* James Brown's Celebrity Hot Tub (Murphy)
* Janet Reno meets Janet Reno (Ferrell and the real Janet Reno)
* It's A Wonderful Life -- The Alternate Ending (Dana Carvey)
* National Terrorist Hotline (Robert De Niro in one of the most hilarious SNL intro bits ever)
* Lazy Sunday aka The Chronic - WHAT - cles of Narnia
* Just about any Celebrity Jeopardy featuring "Sean Connery" (Darrell Hammond)
I must give props to a very recent SNL Weekend Update sketch featuring "Jimmy McMillan" from the Rent Is Too D*** High Party. This short bit finally gave Kenan Thompson something to be remembered for-- it was absolutely spot-on.