I lean towards pure evil villains but either can work if done right. DBZ shines because of it villains and especially Frieza in particular. His personality was based off predatory real estate speculators during the Japanese economic bubble and it shows. He's evil because he's spoiled brat born into an uncontested level of power like most bourgeoisie in real life are.
When humanizing villains it should be done to expose greater flaws, to show how material neglect can lead people to a life of crime and what not. Breaking Bad does this well with it's characters.
