i think that darth sidious was the smartest sith because he fooled everyone and almost wiped out the jedi but i think revan was the least evil because all he was doing was making his galaxy strong enough to fight the real threat in the unknown regions (by taking over his galaxy of course) and i think that darth bane was the first one to be really powerful because he did not share his power with more than one so he had a lot but as u can tell i really dont think anyone was stronger than the other because they al have different strengths
There is no Palpatine. No Empire. No Jedi. There is no Light. No Dark... Just you, and I, here, now.