Who do you think is the most powerful sithlord/other bad guy in all 6 star wars films?Give me a reason why?

It would have to be Darth Sidious. First reason: He was able to darken the force so that the Jedi couldn't read the future.. Second reason: He not only was very powerful in combat, but used his wisdom to manipulate the entire republic and turn it into the empire. Third reason: He was able to seduce Jedi over to the dark side, including Dooku and Skywalker. Fourth reason: He was the first one to use that blue lightening in combat, although in the later movies they made it seem that others had used it before him. Fifth reason: He never was defeated in combat, but lost only when he was betrayed by Vader coming up behind him and betraying him. He was never defeated by Windu, but only looked like it in order to mess with Skywalker.