The best villains are self-aware. They -know- they're villains, or at least perceived as such. They've reasoned that it's worth it. Maybe they were driven to it, maybe they see themselves as saving the world from itself, maybe it's because the Dark Side doesn't just have cookies (even the Light Side has cookies) but also offers triple-dark-fudge-crystallized-ginger-ca
The best heroes are being made. They -don't- know they're heroes, they don't want to be or they never intended to be. They can't be too self-aware, not at the start, or they'd work out an easier, safer path. Heroes are the ones who give up their cookies to someone else because there aren't enough to go around, not the ones who make sure to buy enough in the first place. They can, and must, become more self-aware during the story, and that's their temptation, to see more and more clearly how the path they could choose is always within reach, always right there and so easy to step onto it. The best heroes are on an upward spiral up a steep mountain, barely keeping themselves from stumbling over the edge as the path crumbles around them, hoping to make it to the top in one piece so they can rest.
In a static painting, you can get by with the image of a knight on horseback, armor shining in the sun, and people will label that as a "hero". But when you add the element of time, of story unfolding, then the images to work toward are those of a battered and bruised knight donning armor yet once more, one piece at a time, strapping it to his body, the heavy weight of it clearly shown but taken on for the necessity of it, for the protection of himself and others.
And those are my current thoughts on the matter, for what little they're worth. :-)