It's not even close, really: it's the Master, in almost every incarnation. (I know Eric Roberts is occasionally capable of good acting when he tries ... just apparently not in the TV movie.) Even without the blatantly slashy overtones, he's the perfect foil for the Doctor: the person the Doctor could become himself if he let his power go to his head.
(I'm also very partial to the Zygons and the Kandyman, but the Master is just such an epic villain no one else can compare.)
( the rest of the days )
(I'm also very partial to the Zygons and the Kandyman, but the Master is just such an epic villain no one else can compare.)
( the rest of the days )