I'm going with Bane.
Shocking.
He's a more skilled duelist
👆 I would argue that the gap between them as duelists isn't as large as one would initially think, but it's true that Bane almost undoubtedly is the superior duelist.
with more impressive physical feats.
👆 Galen is far from incapable of handling Bane's physical capabilities though. He was able to hold out against Vader's even greater physical strength, and in turn he was noticeably faster than him as well.
His lightning also impresses me more
👆 True that, being capable of conjuring storms of lightning that can absorb blaster bolts into the storm and melt the blasters of the victims is beastly. Not to mention that his normal lightning was capable of incinerating it's targets and repelling lightsabers. Truly amongst the best in the mythos.
and I'm not quite sure if Starkiller could defend against force drain.
👇 And I'm not sure Bane could even apply it in combat while facing someone of Galen's caliber.
According to Bane in the Book of Sith, Drain is extremely difficult to apply in combat in the first place. Against someone as powerful as Galen I doubt he'd ever get the chance to use it.
In Nihilus's case, your point is invalid. Sion was sitting there beating the shit out of her, they weren't in pitched combat. Of course Nihilus would be able to use it.