In my opinion, evil and love can not walk hand in hand. Anyone who can love, can't be called evil.

- Nuka was essentially after his mother's love and attention. So definitely not he.

- Zira had a "justification" with the unjustified exile she suffered and believing Simba to have killed her obsessive love interest. And she also evidently at least cared for even the child of hers who had felt ignored. So, not her either.

- Whereas Scar obviously wasn't intenting to do evil deeds until Simba grew into an older child, Scar still did them without showing any evident regret. He seemed to murder his brother in cold blood and more importantly; appeared to have no troubles having hyenas tear apart a young child who's even his own nephew.

I don't think Scar is actually evil in the deepest. He just turned evil at some point during the film. He appears one of those "people" who lack emotional abilities such as empathy and other crucials to keep them from doing terrible things. Yet everything he did appeared to be his choices out of free will.

So definitely the most so of the three, because he's not shown to feel any love for or regret of murdering his own family and even a young child.

I think so, mostly because he acted on jealousy/envy/need for power, to the point where he actually killed his brother and attempted to kill his nephew. Zira had reasons to be angry at Simba, considering he pretty much caused Scar's death (despite not killing him as such) and then banished her. I'm not saying that a "nice" person would make the same decisions as her in those situations, but it does at least make it more understandable. (moreso than what Scar did, anyway)

And Nuka only did evil things to make his mum proud. Poor guy.

Zira actually showed love and care. Example: even tho nuka probly wasn't her fav he still loved him and was depressed wen he died