Joyce's death. I think that it effected to all of them. She was a mother figure not only to Buffy and Dawn, but also to Xander, Willow, Tara and Anya. And after her death Buffy had to start take care of not only herself and slaying but also Dawn. She had to be grownup after that... Of course Buffy's death was also very dramatic but when you know that they can't continue the show without her it didn't have that kind of punch to me like there was in Joyce's death.