I used to use the thick soft fur from the belly of a raccoon. It worked great, all underfur with not many guard hairs like you get on the back. They worked great, cost me nothing cause I tanned them myself, easy to put on. Downside was that for bowfishing or in the rain they soak up a lot of water and decrease cast a lot.
On my latest bow I use double cat whiskers. Initially I only put half a pack on my string, but because of tuning issues I found that I needed a little more. I like that by trimming them I can adjust the weight and how stiff or weak the arrow acts. Plus they look cool, and match the black glass on the bow. Also, they are waterproof.