I know I've not been on a lot, but I'd like to add a little something to this.
And the thing I want to add is a little thing I like to call the absolute top tier villains.
Now, this is obviously opinion, but I will say that whether you consider them to be the best type of villain or not doesn't change the fact that they are incredibly difficult to write for. There aren't many of the type I'm about to delve into, and when a lot of people think about the best motivations for a villain, they think of something like Mr. Freeze, driven to his life by severe tragedy and loss, not wanting to do evil deeds, but trapped in this lifestyle and unwilling to part with his own past and let go of the one he loves.
...But there's an even better type.
There exists the rare breed of villain that doesn't just do what they do because they feel they have no option, or have been driven into the life, but rather because they want to make the world a better place. And I don't mean the insane Kefka types who want to destroy the world because 'destruction is the true nature of being' or whatever, or the people who want to rule the planet with an iron fist to try to keep the peace. No, I mean an intricate, well laid plan, the end goal of which may, or even definitely WILL, save millions of lives and create a more peaceful planet. This plan should be so good that, as the story progresses, you begin to be unsure of whether the 'heroes' are doing the right thing. In fact, they may be doing the wrong thing. Generally, this plan will involve casualties or other caveats that make the plan seem, on the surface, pure evil. However, in the end more people will be saved, maybe entire planets or systems or even the entire universe, at the cost of a fraction of the lives that would be lost anyway.
Now, again, this plan needs to be really, REALLY good and, more importantly, it needs to be really, REALLY well explained. Alternatives to achieve the same goals as this plan either should not exist or should be questionably or demonstrably worse than the plan itself. It should be hard, if not impossible, to argue against this thing.
Example: You should read and/or watch Watchmen. If you have, then you know exactly what I'm talking about. If not...just go do it. One of the best written villains of all time. True story.