Just thought this might be fun to do. You can choose up to 5. Please use as many votes as you are comfortable using. I really want to see who gets votes other than a few easy choices.
The list above isn't complete. I limited it to the films, primarily because the list would be too long otherwise, and also because Ward and Kingpin would probably run away with this. For the films themselves, I tried to stick to one or two per film that really drove the action or were a central part of it, not villains that just played a bit roll. I left out those whose "villain" status is somewhat questionable in my mind. For instance, Nebula started out as a villain, but is now a Guardian. Same with Scarlet Witch and Quicksilver not really staying villains. On the flipside, where we have someone like Mordo who we're pretty sure turns to the dark side, we don't really see him do anything villainish in the films, so he is left off. Bucky was an interesting one, because he legitimately flips. But he was squarely a villain during Cap2, even if you want to argue that it wasn't really him doing those things.
Then you have villains like The Grandmaster who are absolutely antagonists, but don't really feel villainy. They just have their own agenda. Kinda similar with Aesha. Yeah, she has it out for the Guardians. But she doesn't really appear to be evil, and isn't really bent on taking over or destroying.
Anyhow, have at it.