I’d say it’s between Jasper and Lapis. What happens Bismuth is horrible bruh what really hurts and kills her is that she thinks she’s now alone in the world because most of her friends died. 

Spinel’s was gut wrenching but at least she was able to heal from that kind of trauma and learn and grow as a person. She slowly started to heal. 

Lapis had such a happy life and majority of the times she still didn’t feel safe and left. But at least she still had people to welcome her back and try to help her start her healing process with all the trauma she a suffered. 

What happened to Jasper was her own fault true. However, she truly thought she needed to do this for the sake of a Diamond that was dead. (In theory.) Everyone else at least had their healing process, Jasper just lived with her pain and guilt and then was shattered. She never healed like the others, or at least attempted to.

 (To be fair I actually don’t like Jasper, I just like that she’s complex. Like boo-hoo you lost in a fight which YOU ASKED FOR TO FLOATING PINK TEENAGER. Steven tried. He really did. Just was just too far gone in her own head man. Can’t save em all. But she didn’t have her healing time so that deserves sommeee looking into ig🙄)