I generally think the blends look nicest as they combine a bit of loft from the synthetic fiber with the definition & flatness of cotton. Fairfield makes some lovely battings. They have a 50/50 cotton/bamboo rayon called Nature-Fil. By using cotton blends, you have the option of steam blocking (my preference) versus wet blocking the quilt. I haven't personally worked with Nature-Fil due to an allergy to rayon, but I've seen it in many quilts & it is quite stunning. I've worked with Fairfield's 80/20 cotton/poly blend called Fairfield Cotton Classic. It is also quite lovely for wall quilts & can be steam blocked.