For being ridiculously powerful, i am going with Lord Vitiate. Old Republic emperor of the Sith. He consumed the force energy from every living being on his home planet. Completely destroyed it by feeding on every shred of force energy on the entire planet. Yes his end game was to consume the entire universe and live forever, but For what he could do, he has to be the most powerful Sith ever.
The very existence of flamethrowers proves that some time, somewhere, someone said to themselves, "You know, I want to set those people over there on fire, but I'm just not close enough to get the job done." -George Carlin