Is the Zweihander the best, no cost to use, melee weapon in the game?
I have always thought that knuckle dusters are the best choice of weapons since they get bonus damage that scales with physique.
Is it because Zweihander has high base damage and so any damage bonus with that scales better?
The damage on the Zweihander is almost always going to be better, mainly since dual-wielding has no real value versus using a two-handed weapon outside of some super uncommon damage type resistance/immunity situations. The knuckle dusters aren't even the best unarmed weapons you can get your hands on; the clear demonstones have better damage than it.
The only circumstances where the Zweihander gets out-muscled is if you're specifically playing a taur/feral, which adds an additional 40 base damage for a total of 60, and/or you're using Cloak of Flame at max level to add another 50 fire damage to your unarmed attacks, which goes over the top of it. For all practical purposes, though, it's significantly cheaper to simply get a Zweihander and then kill 95% of enemies in the first turn with a giant crit, especially since you don't need to reach physique cap to make the most of it.
