So favorite star wars antagonist here?

good choices there,

I go with slimy old Palps too - one of the only antagonist who really kicks ass and wins - at least until Ep 3 and his tactical oversight of  few warmongering teddy bears does not count.

As a second I take Asajj Ventress because SW sourly lacks female antagonist (females tend to be idealized, flat and lame in this universe) and she was really a cool character with a good arc. 

Vader and Palpatine! Everybody else may be cool but just second tier:

- Vader wins on the execution front: better suit, better musical theme and better voice/breathing than Palps.

- Palpatine wins on the writing level: he is a consistently scheming guy who knows what he wants and when to destroy his pawns, allies and enemies. His political scheming and character is Lucas smartest, most inspired writing by far.

Vader is very inconsistently written as a character: Ep4: uncharismatic mid level executioner/henchman with a score to settle; Ep5; demonic villain who wants to overthrow his emperor, Ep6: conflicted, old man who must serve and defend his master/Emperor. 

Most other franchises would wich to have only one villain so good.