The biggest issue facing Bane is Gethzerion's adept skills with lightning as that is his vulnerability. Gethzerion's weakness is that from what's been stated of her though she does use a saber, her skills with it are nothing noteworthy.
This would be a relatively close-in encounter so it'd be great if someone could post more on Gethzerion's melee with Luke and such. Both Bane and she have some pretty impressive feats in the Force, and despite what Bane showed in orbs, I'd like to see a little more info before I declare my thoughts on a winner.