Both the light side and the Dark Side exile could do it. the DS exile is the only one that did it, because well really he's the only one that had the chance to do so. And the need to do so. Kreia could do it perhaps I am not sure... She could rip the force from people but probably not in the effect that the Exile could let alone stand Nihilus. But who knows you can't be sure about that. I see no real reason to believe that she can actually.
And on who will win DS or LS Exile... Probably DS more combat experience.