Day 2: Favourite Episode This is hard but I note that it is favourite and not best so instead of "Hush" or "Once More With Feeling" or "The Body" or "Innocence" or "The Wish" or even "Doppelgangland", I say it's "Who Are You?".
I just adore this episode.
It has everything: Sarah Michelle Gellar at her best, fabulous dialogue from Joss, lots and lots of Tara, a thinly disguised metaphor for sex, the word stevedore, "tiny, tiny babies", rubbish English accents (ok, that's not adorable), "because it's wrong" and Faith and Buffy beating each other up.

Hard to choose favourites amongst nearly 150 episodes, but I have to go with "The Gift". Buffy diving off the tower into the electric blue portal has to be the money shot of the series, IMO.
BtVS never fully recovered after that episode.