Luke, with difficulty. And GV, here's something: find the quote which states that it takes the combined potential of Luke, Leia, and Anakin to tackle Sidious. Go ahead.
I say the duo win. Kyp could hold off Luke until Sidious managed to launch a Force Storm. Then I don't think Luke could block the storm because, if nothing else, he wouldn't be able to block it and hold off Kyp at the same time. So he would die.
Luke. He's much more powerful than he was in DE. He can take DE Sids easily, if he's alone. It will be difficult to fight both him and Kyp, but in the end he still wins.
Faunus, GV doesn't understand, nor did he read the comics, which is why the Sidious fanboyism is coming into play. Wake up from your dream world Neo, DE Luke=/DN Luke. And there was no talk about potential anywhere, that's just some nonsense you and IKC made up because you didn't read the comics, and you dislike luke.
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Facts, the Anti Fanboy solution
Except for the fact that you don't know how long it really takes Sidious to conjure up a force storm, except that they have to have a considerable distance between them, and you're forgetting the fact that Luke can chunk them into a black hole or the nearest star before Palpatine creates the force storm. Then again if it is saber combat, Luke ends it quickly.
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Facts, the Anti Fanboy solution
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I think Kyp could hold off Luke long enough for Sidious to get a good attack against Luke. I don't think Luke could hold off a force attack from Sidious and a lightsaber attack from Kyp. It would be a close fight, though, now that I think about it more. If Sidious could conjure up a force storm, then I don't see Luke winning, if he could eliminate either Sidious or Kyp early, though, Luke would win. Where is the fight?