I think it depends what you're looking for. For example, do you want to emphasize piecing or quilting? If it's quilting, go with wool, if it's piecing go with a blend - cotton/poly, cotton/wool. If it's strength you need, go with Warm & Natural. If you're going to hand quilt it, go with Hobbs 80/20 or a thin Dream cotton. Other considerations, is it going to be washed many times or hung on a wall, and above all, what is your own personal taste. You may also want to consider, depending on your project, how far apart the quilting can be.
I am in the process of trying several different batting and have yet to figure out my favorite. I can tell you for sure, with everything else being equal, different battings will change the overall look and feel of the quilt.