Angel: A Hole In The World / Shell
I see these two episodes as a big extended episode and while we grieve for Fred in this episode, I love the tragedy of it and everybody on the cast brings their A-game. It's an incredibly good and well-written storyline. I also love Angel and Spike get closer in this episode.
Buffy: I Only Have Eyes For You
Objectively, there are better episodes than this one, but as a Bangel shipper, I have a soft spot for the melodrama of this one. I also love the scene where Giles talks to Buffy about forgiveness.