Edit: Let me edit my whole statement.
NONE because they were nothing but pricks but if I had to pick, Vanitas and Isa because I have a soft spot for them though their abusive behavior shouldn’t be excused at all.
Edit:
It’s kinda funny that people bash Vanitas, a child, for his shitty behavior and dismiss his redemption arc but go easy on Isa, a grown man, for his shitty behavior. Both are wrong regardless but I’m just observing here. Saying Vanitas shouldn’t be his own person because he’s evil is f*cked up to say and so the main observing component in what chooses who lives and who doesn't is their ethical compass/how we see them? My point is that saying he shouldn't live to be his own person just because he's evil is shoddy and I like to note that I was more happy to find out that he was resurrected instead of being brought back through time travel, he got a second chance to live and Vanitas returning back to Ventus would ruined KH theme about “being your own person†and it wouldn’t make sense for his resurrection either. Also Ventus has no qualms for Vanitas at all, he doesn’t want his darker half back but I am expecting a “resolution†between them. At the same thing, I don’t want Vanitas and Ventus to have a relationship because it’s so toxic regardless being connected to each other and they should seek their own paths.
Besides Saix/ Isa (actually we don’t know if he was brainwashed) The only person I see being brainswashed and molded by Xehanort is Vanitas. Unlike the rest of the villains, Vanitas was an empty creature at birth (whether he had Ven’s memories or not) stated by Xehanort and he was raised and trained to do evil things by an evil man who also wants to destroy the universe. His life was focused around a purpose and only one purpose: one given to him by his creator and that purpose was to create the X-blade. Vanitas didn’t have a choice at all but overall, he still have his own will and he made his own decisions. (His actions are definitely not excusable btw)
The reason why I am sorta soft with Vanitas because his first life was dominated by Xehanort. He never truly had the opportunity to pick, all alone terms regardless of whether he needed to be a piece of this. He had somebody boundlessly more older and more powerful than him, his creator, his master, breathing down his neck and controlling his life from the minute he were conceived and all of our other characters have had some form of happiness while Vanitas was stripped away from his lighter half, he doesn't have friends or anybody but Master Xehanort. I am additionally sorta soft with Vanitas that because due to his unstable creation, he's not by any means fit for feeling positive emotions and it must suck to just have and just to feel negative emotions. Having your feelings spill out from your body for the rest of your life must suck. I liked Zip’s (or what is it Alpha?) idea with Vanitas’ heart being balanced with light and darkness which would eliminate the unversed existence and Vanitas would learn etc etc etc
The gag is....I like Isa and Vanitas as villains so I’m conflicted
Edit: Okay. So didn’t Nomura confirmed that Luxord, Saix, Xigbar, Larxene, and Marluxia were turn back into nobodies? If we destroyed them, wouldn’t they turn back into humans? Lol