Easily Colonel Yellow. His plan to usurp Tony's position as the Grrrreat Tiger was absolutely diabolical.
In all seriousness though, it's Piccolo Daimao by far. Him wanting to see humanity tear itself apart through lawlessness ties in well retroactively to him having seen the evils of humanity prior to his split and, even on its own, is a more interesting motivation than other villains have in their conquest and destruction. Hell, you could even argue it's enough to have him be the best villain in the franchise if looking at all aspects of it, considering how much Super tarnished Freeza.
Tao Pai Pai could've been a contender with how much of an absolute Chad he was in his introduction, but all that was diminished by the way he acted when Galu surpassed him and how his return was used purely to develop Tenshinhan rather than further Pai Pai's own characterisation.