Sidious. He is supposed to be evil incarnate. He also has absolutely NO respect for anyone or anything except for himself. On a scale of one to ten:
Sidious - 10 the Star Wars Hitler * 1000
Bane - 9 murdered an innocent family for no reason other than to feast on their suffering, kills just about everyone he sees, thinks that honor is a lie, given a 9 and not a 10 because he seemed to create the ROT despite knowing that he'd not live to see it but was content with the sith ruling the galaxy some day (so it wasn't 100% for himself plus he didn't mind that Zannah would one day kill him) and because he used to be pretty nice before getting corrupted
Dooku - 6 he thought that what he did was right, but he still helped start a war that killed billions
Vader - 7.5 a total badass but he turned evil for a good cause (to save his wife isn't an evil reason) and redeemed himself in the end)
Caedus - 4 had a family that he cared about, was for the most part nice to his officers, consciously tried to avoid becoming like Palpatine and did what he did for a noble cause (but with a bad method)