Naesala would do 18 Dmg, assuming his weapon is at SS, and Tibarn would do 34 damage (also assuming his weapon is at SS).
Gameplay stuff aside, it's been said in the games that Tibarn is stronger than Naesala, and Tibarn's strength is something legendary (this is implied in things like "When our king attacked him, he didn't even budge!" [not exact, I know] when talking about Zelgius). Also, Naesala fears Tibarn. That's gotta say something about him.
Sooooo...yeah. The debate pretty much ends here.