As for candidates, I think Russell should be taken off. Had it not been for Rutherford and MacMillan, his movement would've been a historical footnote. Seeing as how Russell's ideas have been mostly discarded in present doctrine, and he is not given much mention aside from the Proclaimers book, I think has had the least influence on modern dubs.
IMO, the greatest villain would be the one whose policies continue to inflict suffering on people, or continue to cost lives. The blood issue and the disfellowshipping practice are the only things that accomplish this.
Arbitrary disfellowshippings are wrong, no doubt. People have committed suicide over it, so it does lead to loss of life. This pales before the blood issue, for which people are still losing their lives. Therefore, C.J. Woodworth and any who helped form the JW blood doctrine are in my eyes, the most villainous.