Not the most powerfullest but your greatest. The one you have given the most attention to. The one that has, in your opinion, has the best story behind him/her. Post your character with the history and powers.. =)
Well in some of my stories my best and favorite villain to write with my cousin is Augrath. Augrath is a giant fiery planet that originally went by Scorch. but a reckless king named Augrath tampered with an experimental cosmic weapon and an energy surge cause his body and powers to be merged with the planet. The planet gave him amazing Psionic abilities capable of warping reality. With this power he erased all sentient will from the creatures living on his planet and uses an avatar called the voice of Augrath to do his bidding and aid him in killing of all sentient will in the universe leaving only "Augrath" to rule. Serving as the worst and biggest treat for the Superheroes of Earth
Psionics - Creation, Mind Control, Matter and Reality Warping, Telepathy Telekenesis.
Enemies- The Squadron, The Brave, The Children of the Five, The Omegas, Colu
Edward Marx- Sociopath. Monomaniacal. Telepath. Psionic viral vector.
Think about giving all the power of the high end Marvel telepaths to a guy that has nothing at all that he believes in other than amusing himself and he's got an ugly sense of humor. Also everyone that he comes into contact with he leaves a little of "himself" behind and it becomes a slow psychic cancer that eats the mind making serial killers and butchers, if you're lucky. If you're not, you spend the rest of your life staring out of eyes you can't control in a body that doesn't respond. You get to be a conscious vegetable.
Probably Honor Avenger. She has her own city, a well constructed backstory, heck, she killed a great hero in the Vine and a whole team formed just to stop her. Guess that makes her better than all my other villain accounts combined. Even more so as she is dwarfed in super powers compared to the others.
Victor Ross. Not for accomplishments past, but for what I've got him tied into that's yet to come to light. In fact, if it did become known, he'd be tied to some pretty gruesome acts. And the fact that he's just cold, ruthless, efficient intelligence. No ego or overconfidence to limit him. It really gives this sense that even as a mortal man, he's incredibly dangerous, and he's capable of some pretty nasty stuff.