There are so many great and absolutly mind blowing episodes of Buffy that you can't possibly choose just one... i choose all of these lol
Never Kill a Boy on the First Date (Wills, Xands and Buffs talk on the fountin was classic lol)
Angel
Nightmeres
School Hard
Halloween
Whats My Line, Part One and Two
Ted
Suprise
Innocence
Bewitched, Bothered, and Bewildered
Passion
Becoming, Part One and Two
Faith, Hope, Trick
Band Candy
Lovers Walk
The Wish
Amends
Bad Girls
Doppelgangland
Earshot (Simply for Buffy finding out about Joyce and Giles)
The Prom (It was touching to know people actually noticed Buffy as a protecter to them)
Graduation Day, Part One and Two
Beer Bad
Pangs
Something Blue
Hush
A New Man
This Years Girl
Who Are You
New Moon Rising
The Yoko Factor (Angel kicks Rileys ass)
Primeval
Buffy vs. Dracula
Family
Fool for Love
Into the Woods (Riley leaves! yay!)
Triangle
Crush
The Body
The Gift (It was a touching episode that made me cry)
Once More, With Feeling
Tabula Rasa
Smashed
Gone
Entropy
Seeing Red
Grave
Same Time, Same Place
Selfless
Him
Conversations with Dead People
Showtime
Potential (Dawn and Xands talk was sweet.)
Storyteller
Lies My Parents Told Me
Dirty Girls (Faith came back)
Touched
End of Days
Chosen (The End of Something Great)