I think Kamsa is the most evil than other. He snatch the power and hurt the people with out reason even try to kill baby. Even planned to kill 11 years old krisna. He showed no mercy at all. Ravana and Hiranyakashyapa showed mercy and values in their behavior.
All are equally evil.I believe their destiny was to be evil under larger scheme of things by Creator.All these were finally destroyed by God himself just to teach world about evil.