I use both but prefer to use Big Fly Fiber on my muskie flies. Not terribly too much difference though, imho.
I'd pick up some of each and try it yourself. The B.F.F. goes on my topwater Mega-Divers and the I.S. Hair goes on my streamers.
http://www.greencaddis.com/product_i...2fe34c717e1a1b
Have fun with both. Good stuff.
Jeremy.