ANGEL:Spent hundreds of years, tortured in a Hell Dimension to the point of insanity for what he did just in Buffy Season Two.
SPIKE:Spent weeks in a high school basement, racked with every bit of guilt and later beaten and tortured by Wood, not to mention the chip in his head going off without even having to hurt another human. He went through a lot of pain when you think about it for what he did
WILLOW:Lost the trust of her friends and had to spend time with Giles. Think about it, when flayed bodies started showing up who did they start blaming? Her! Even though she had nothing to do with it, they just assumed.
ANYA:Well, she's dead. She had the option to run from the apocalypse but she stayed behind and fought which ultimately led to her demise
FAITH:She spent time in prison! Willingly. And even then she was still regarded as a rebel slayer, still criticized by everyone around her.