It's in chronological order but I have starred my favourite.
1. "Prophecy Girl"
Season one BtVS is a lot of fun and often very enjoyably silly but it hasn't ramped up the drama yet but there are two scenes (Buffy quits and Willow and Cordelia discover a room full of murdered students) in this episode that make you realise that there is enormous depth as well as zingy dialogue.
2. "Surprise" and "Innocence"
"Surprise" is just the starter before the main course. SMG continues to amaze as an actress but she is outstripped by an utterly adorable Alyson Hannigan who in "Innocence" establishes herself as the reason why I started to love BtVS. Her scenes with Nick Brendon and Seth Green are wonderful.
3. "The Wish"
This is an alternate reality and, of course, it's going to have a happy ending but Willow and Xander are so mean, Cordelia is murdered by them and Buffy gets her neck broken by the Master. It's so deliciously horrible.
The funniest episode of BtVS which is full of superb dialogue and great acting. Willow as Vamp Willow waves at Oz and she is so endearing. And let's not forget she's "kinda gay".
5. "Graduation Day, Part I" and "Graduation Day, Part II"
Buffy tries to kill Faith. That is all.
Sometimes when something as a reputation as being one of the greatest, if not the greatest, something or other then I have the tendency to grab the word "overrated" except that this isn't. We have scary villains, an overhead projector, suggestive miming, an exciting chase, a thrilling fight in a clock tower and my top BtVS moment as Tara and Willow link hands and make magic.
7. "Who Are You?"*
“I am you know”, "And you know why I don’t? Because it’s wrong.", “So Willow’s not driving stick anymore.”, "Plus, she was, um, she was kind of mean.", "I trust you", “What’s a stevedore?”, “You’re nothing! Disgusting! Murderous bitch! You’re nothing! You’re disgusting!”
8. "New Moon Rising"
This is certainly not among the best episodes of BtVS but it has hand holding, "overhelping", a reminder of why Oz was so great, Willow's coming out and an extra flamey candle.
I don't love this but is a tremendous piece of TV.
10. "The Body"
This surely has to be on any list of best episodes.
11. "Once More, With Feeling"
Another audacious episode from Joss Whedon. "Going Through the Motions", "I've Got a Theory/Bunnies/If We're Together", "Under Your Spell", "I'll Never Tell", "The Parking Ticket" and "Walk Through the Fire" are the musical highlights.
12. "Tabula Rasa"
For some people this is the episode that almost literally jumps the shark but I love it because a) it's a very funny episode topped and tailed by two heartbreaking scenes, and b) this was when I fell for Tara (and Amber Benson), I felt so bad for her hurt and sadness that I realised I totally loved the character and that she had inched her way into my heart.