Nihilius would just force drain Bane and Zannah. Plus Nihilus is essentially a mindless hungry force cookie monster, so Zannah probably can't give him nightmares

Markas Ragnos is where its at. I wanna see him do something as a living, breathing sith lord. For all the sith lords before Revan, we mostly see them as ghosts or running away from their failures (ahem naga sadow)

Nihilus and Sion would undoubtedly win in most of these situations, although, Nihilus would get most of the credit

Give Sion a participation award, he clearly tried