S1 - Prophecy Girl. It showed just how vulnerable yet strong she is. It really gave you your first real look at who Buffy is inside. Who she wanted to be.
S2 - I am going with Halloween mostly because it was a lot of fun. I can watch it many times over and I think people who are not yet on Buffy would really enjoy that episode.
S3 - So many good episodes in s3. It's hard to choose one. I want to say the prom, but I want to say doppelgangland, and want to say the wish. Any of these including Faith Hope and Trick would be good to show anyone.
S4 - Something Blue is just so funny who could leave that out right? But, New Moon Rising is a brilliant episode so I would watch that over SB. In the end, Primeval is tops out of the three because Buffy beating Adam and Giles Willow and Xander helping to back her up in the way they did. That's something beautiful. But I still need to choose Hush. It's a mini horror flick that is very enjoyable and unique.
S5 - The Gift. Once again we see how selfless Buffy can be. She really is a hero. If anyone had anything bad to say about Buffy before this episode, they have no right to say it after.
S6 - OMWF is the most fun, but a close second is Tabula Rasa. I think the two go hand in hand. They are my choices for season 6. But since I should only choose one, I choose TR.
S7 - Chosen. Again, brilliant. But this time it's not just Buffy being strong and brave. It's a handful of young women who had faith in themselves. Who were giving their lives to protect the world. They are all strong even before becoming slayers. Just in a different way.