Anakin is the chosen one. He brought balance back; just not in the way the Jedi thought.
Aye, he balanced it right down alright. 2 Sith and only a handful of Jedi. Maybe the Jedi scholars should have done some more meditating on the prophecy. I would say though that probably Emperor Palpatine was the most powerful Sith. He used Sith Meditation to cloud over the perceptions of all of Coruscant in order to land and hide the Super Star Destroyer Lusankya. He was also the culmination of generations of Sith training and planning.