With a nod to Makuta, I'm here to stand up for The Fire Lord (not Ozai) from Hero Factory. In terms of motivation (because "best villain" is a very subjective term to be honest) I think he was one of the more interesting villains ever did (or has done?) I mean I think that great line of his from "Ordeal of Fire" sums it up:
"Once you taste the power, you can't stop. What is evil more than wanting something so much you'll do anything, hurt anyone, to get it?"
He wasn't a conqueror or power hungry (well I guess he was, but different kind of power), he was a simple mining bot who became corrupted and started doing evil things until he didn't have a say in the matter anymore. Which raises the question, how evil is someone really when their free will has been overridden? When they can't stop doing evil because there's something wrong with their circuits that it's all they can do.
Yeah, I know they're lines in "Ordeal of Fire" that show that the Fire Villains liked being bad, I get it; they're villains written for a kids show/franchise. They shouldn't be expected to be perfect or super deep, but I think they deserve some credit all the same.
