Who is the greatest sinner?

Chillingworth would probably be considered the biggest sinner because his sin was meant to exact revenge. Hester and Dimmesdale sinned, but they hurt themselves more than anyone else. Chillingworth's sin was meant to exact punishment. In Dimmesdale's words;

“I freely forgive you now. May God forgive us both! We are not, Hester, the worst sinners in the world. There is one worse than even the polluted priest! That old man’s revenge has been blacker than my sin. He has violated, in cold blood, the sanctity of a human heart. Thou and I, Hester, never did so!”