I would consider the old sith lords were superior in terms of battle that is. Like Marka Ragnos and Exar Kun. If you remember on Korriban, Kreia explained that these sith lords were so well experienced with a light saber that the current sith lords and jedi masters would be considered as mere children playing with toys, to them. Now in ways of manipulation and the force, Kreia was indeed powerful. But she herself was corrupted. For someone to hate the force was just maniacle. I wouldn't even consider her a Sith Lord because, the Sith Lords themselves consider the force to be a powerful weapon, to help them gain victory. Now Revan's intentions were never fully clear. No one knows whether he fell to the darkside for his own ambitions or if he was trying to protect the entire galaxy from a greater evil, thus eventually venturing into unknown space. So, perhaps Sideous wins by default :D