IF you decide to pre-shrink your batting, make sure it has a scrim on it first otherwise you'll have nothing but a bunch of loose fluff.
I personally prefer an organic batting, so far I've only used cotton (warm and natural). I like the organic batting because it breathes unlike polyester, but from what I hear the cotton/poly blends (80/20) are pretty breathable as well.
I just purchased some wool batting on sale recently but have not had an opportunity to use it yet. The wool batting seems to have more "space" or "air" in it than the warm & natural batting, and it's thicker - but overall lighter in weight and the drape on it is much more to my taste (nice and supple - whereas W&N can be quite stiff especially when quilted heavy which is my preference).
I adore wool clothing because it keeps me warm, but cool - if you know what I mean. I am rarely too hot in wool because it breathes with you - even more than cotton. And it's more absorbant and wicks any perspiration away from you. In the winter I live in wool socks (a trick I learned from my father) and my feet are always warm. Under normal conditions my feet sweat a lot (genetics I inherited from Dad), and because they sweat they then get cold because they are wet. Cotton socks just get wet and stay wet - the wool socks wick the moisture away from my feet and my feet remain warm and dry. I'm hoping the wool batting will perform the same way and when I *finally* make the quilt for my bed my husband will not get too hot and I will not get too cold.