Tragic villains without a doubt for me.
I am an addict of crime thrillers so I like twist villains and recently I watched animated shows with great twist villains.
Tragic backstory trope is overused to death at this point making genuinely tragic backstories disinteresting. I am getting tired of cliched backstories like "society killed my parents so I became evil" or "I was abused in childhood so I became evil". Not saying they are bad motivations but they are overused to the point where they are not compelling anymore. It also spreads unrealistic message that all people are good by default and that people turn evil only because of external factors. It is possible to craft great villains without tragic backstories and not make them feel generic. I think this was why I liked Chameleon's backstory because it felt unique and it was a tragic backstory that was actually realistic but too bad people will just label it as a joke or lazy writing.