My decision on batting for a quilt depends on what kind of look I want when finished and washed. Poly will not shrink, so your quilt will not have as much of the crinkly look after washing, which is great for dressier quilts where a smooth look is preferable. 80/20 blends will shrink just a bit, but has a softer feel than 100% poly. 100% cotton batting will have a shrinkage that averages between 3-5 percent, which gives you the crinkly look and a very soft quilt after washing. Just as others have said, each batting will have different quilting requirements, so make sure that your SITD (stitch in the ditch) is close enough for your batting. Those are the three main battings, but each has many variations. There are also more battings such as bamboo, wool, etc....each having different applications. I myself like Hobbs Polydown for a thicker feel, but also like the 80/20 blend that I can buy at WalMart.