I don't think I have ever tried Yak hair, but I do have an Alpaca hair rope that came from Peru. I do not like it because it is too light for the diameter. Not sure how that compares to Yak though.
We traded some cow freight for a couple of Helen Dougal's hair ropes this weekend. And we ordered another from her. (she only makes them in warm weather)They have an awesome feel!
I say stick with the horsehair but it depends on who makes them. I have one I bought off of the internet for my husband because it was the color combo he loves to replace a Schutte that is completely worn out and been retwisted a half dozen times and it feels horrible! All hair ropes are not created equal! LOL
I DON'T LEAD 'EM AND FEED 'EM, I RIDE 'EM AND SLIDE 'EM.