Years ago, in a television interview, actor Vincent Price was asked, based on his career in horror films, what he considered the most frightening Hollywood Movie Monster was.
His reply: "A man without a conscience."
The Denarians that are so subsumed by the dark angels in their coins don't count; they're more animal than human.
To me, Nicodemus himself is the worst of the lot for the reason Price pointed out. He's a man - intelligent, educated, utterly ruthless and all but devoid of conscience (issues of his daughter aside). He is capable of truly horrific acts that would be found few other places... certainly nowhere in the natural animal kingdom on Earth. One would have to go to the realms of the supernatural to find equal or worse.
Just a thought