I'm afraid the list is a bit size-queen oriented.  It presumes that power and dominion equal greater evil.
My assessment of evil is more personal.  I think a human that intentionally grinds another into misery and holds him or her there, on a personal and day-to-day level, is more evil than a man who simply makes a despotic decision about faceless populations.
Michelle Crockett would be on my list.  Her abuse of her daughter Danielle will chill your blood.  I once helped three children who were living in conditions just slightly better than the home described here:  
http://nypost.com/2008/08/10/girl-found-in-horror-closet/
Oh, and if you don't read the article, Michelle didn't serve any prison time for the 20-year-sentence due her crime.  Prosecutors dropped the prison time in order to coerce her into giving up custody of Danielle.  Horror.
Jacole Prince deserves a seat of honor at Hell's head table.  Her treatment of her daughter was equally untenable:  
http://www.kshb.com/news/local-news...-concerns-about-lp-early-in-little-girls-life
Barbara and Kenny Ray Atkinson also merit Dishonorable Mention.  The horrors they knowingly inflicted on the Lauren Kavanaugh are beyond the comprehension of most of us:   
http://www.dailymail.co.uk/femail/a...tortured-forced-live-wardrobe-FIVE-YEARS.html
There is a long list we could make.  I don't think one person truly exceeds the rest in evil.  Once they get to this level, they are all equal and should be burned up and removed from the living.  There is no return from this deep depravity.  It is not ignorance, but evil, to be sure.