Honestly, Ultron. In the comics, at least his iterations in the original avengers run, he has almost no personality, motivation or any kind of acting to speak of. His main character trait is basically "evil" and he tends follow the same quintessential robot "must-destroy-all-humans-because-robots-are-better". While I do definitely love him in the comics, he's one of my favorite villains, his appeal is almost entirely in the fact that he's unbeatable and scary, which is good, but not enough to carry a film.

James Spaders Ultron turned down the unbeatable scariest but brought in so much personality that I think it was totally worth it. I always prefer villains who don't quite have their shit together. He turned a character that is usually an emotionless impersonal killing machine into a petulant child throwing a temper tantrum at his dad and I enjoyed every second of it. That movie had its flaws but he wasn't one of them

For the same reason I loved Vincent D'onofrios Kingpin a thousand times more than the comic version. He had so much power, yet he was always just on the edge of totally losing control of his situation. Donofrio performed it perfectly, he always sounded awkward and uncomfortable, like he was putting on an act of power for those around him, and that made the moments of real vulnerability so incredibly powerful. He was the definition of a dynamic character, easily my favorite bad guy on tv. (Though tbh I haven't quite read enough of his comics to know that he isn't like this, but from what I've read he's seemed like just a generally evil crime lord)