The type of batting you use depends on a couple of factors, price is one but seldom the main one. Most people that I've delt with prefer 80/20 (thats 80% cotton & 20% poly). 100% cotton is good as well because it breathes, and there's Bamboo cotton blend, Soy blend and wool.
Last of all there's polyester, which is cheapest of the lot.
Lanny