First: There is already another thread about this here
Second: I think your question would be better said like, "Who
is the most powerful Sith?"
Third: Please learn to spell, and use the spell check. The names of the Sith Lords that you have in the poll are correctly spelled this way.
Fourth: From now on, please don't vote for every option in the poll.
And in anser to your question, I would say that Nihilus is the most powerful.