From least to most
5. Genovese. They've never had a Casso, Gotti, Scarfo, ect. And only seem to kill when it's absolutely necessary.
4. Luchesse. Aside from the Amuso/Casso era, they were peaceful by mafia standards.
3. Gambino- Violent during Anastasia and Gotti years. Also had DeMeo crew
2. Bonnano- Always seem to be violent.
1. Colombo- 3 family wars