What is the best tsuka material?

As a discerning enthusiast of traditional martial arts weapons, I'm curious to know what the consensus is on the optimal material for the tsuka, or handle, of a sword. Is it the durability and grip provided by hardwoods like oak or maple? Or perhaps the elegance and balance of rayskin wrapped in silk? Or could it be the modern alternatives, like carbon fiber or even synthetic materials? I'm eager to hear your thoughts on what truly makes for the best tsuka material in terms of both functionality and aesthetics.