Originally posted by Gideoni just read the part where you said "sidous would definately make this list"!
Ranking the Jedi and Sith in terms of power is an impossibly difficult task, even if you subscribed to a comprehensive analysis of canon. There are certain placements, however: Darth Sidious has displayed a far greater command of and strength in the dark side of the Force than any other Sith Lord in history; his status as the most powerful Lord of the Sith is documented by numerous sources. The RotS novelization regards Yoda as "the most devastatingly powerful foe the darkness had ever known" -- making it quite clear that, as of the prequel trilogy, he is more powerful than any Jedi before him.You have individuals such as Luke Skywalker, who has, at various times, demonstrating a command of the Force on par with or surpassing Yoda or Sidious, yet aren't given any accolades by proper sources. Jacen Solo is someone who hasn't truly demonstrated a great destructive or offensive power, but has been cited by various sources as "second only to Luke" in terms of strength in the new Jedi Order (putting him above Force titan Kyp Durron), wielding power that has "even surpassed his grandfather, Darth Vader" (a Sith Lord whose potency was 80% of Palpatine's own), and "the most powerful of the Sith Lords."
The Complete Star Wars Encyclopedia credits Exar Kun and Darth Plagueis as being two of "the most powerful" Sith Lords in history, despite -- in the case of the latter -- having no feats to his name. Marka Ragnos is another highly regarded and feared Sith Lord despite nothing to gauge his powers on. Other than that he was the most powerful of the ancient Sith.
Individuals like Count Dooku seem to possess a greater refined skill than any true raw strength; Yoda cited him as the Temple's greatest and most learned student and the RotS novelization regards him as "one of the most powerful Jedi in the Order's 25 thousand year history" and "an even greater Lord of the Sith," suggesting an incredibly high placement. Darth Vader seems to possess great telekinetic skill and incredible raw strength, being 80% of Sidious in terms of power and possessing a greater command of the Force than Kar Vastor (who is regarded as being on par with Yoda and Anakin; Emperor's Hand Cronal regarded Vastor's connection to the Force as "astonishingly powerful"😉.
In short, it's really hard. What is certain is pretty much only that Sidious is the most powerful Sith ever.