I judge these by what we would think of them if they were real life people.
1.Celestial Dragons/Gorosei/Imu (Goes without saying)
2.Big Mom (Genocide of an island for not delivering candy, Chaotic Neutral, sociopath)
3.Akainu (Participator and facilitator of the genocide of a whole people)
4.Aokiji (Participator in genocide of a whole people, yeah motherfucker I didn't forget)
5.Crocodile/Kaido/Orochi (Enslavement of entire nation/Holding nation hostage by limiting food/water supply)
6.Doflamingo (False flag slaughter of innocent civilians in order to become the ruler of Dressrosa, Major figure in the slave trade, sociopath)
7.Rob Lucci (Massacred innocent soldiers held prisoners, will do whatever evil that WG tells him)
8.Caesar Clown (facilitator of child experiments)
9.Arlong (Just because you were hurt in the past, doesn't give you the right to do the same to other people)
10.Black Beard (Chaotic neutral/sociopath/Will occasionally do evil if it can further his own goal in the pursuit of becoming pirate king but hasn't been shown to kill or hurt any civilians)
I might have forgotten some but these are the 10 that come to mind out of the major characters.
1.Celestial Dragons/Gorosei/Imu (Goes without saying)
2.Big Mom (Genocide of an island for not delivering candy, Chaotic Neutral, sociopath)
3.Akainu (Participator and facilitator of the genocide of a whole people)
4.Aokiji (Participator in genocide of a whole people, yeah motherfucker I didn't forget)
5.Crocodile/Kaido/Orochi (Enslavement of entire nation/Holding nation hostage by limiting food/water supply)
6.Doflamingo (False flag slaughter of innocent civilians in order to become the ruler of Dressrosa, Major figure in the slave trade, sociopath)
7.Rob Lucci (Massacred innocent soldiers held prisoners, will do whatever evil that WG tells him)
8.Caesar Clown (facilitator of child experiments)
9.Arlong (Just because you were hurt in the past, doesn't give you the right to do the same to other people)
10.Black Beard (Chaotic neutral/sociopath/Will occasionally do evil if it can further his own goal in the pursuit of becoming pirate king but hasn't been shown to kill or hurt any civilians)
I might have forgotten some but these are the 10 that come to mind out of the major characters.