A lot depends on the finished look I am going for and who will be caring for the quilt. I still like poly for baby or children's quilts as it launders well and is lighter. I also like poly if I want the quilting to really pop. Now that they make the thinner poly it is easy to work with by hand. For quilts that may be around forever or a client's special quilt I use Dream Cotton the thinest they make. It allows me to make the smallest stitches. It is all a matter of personal taste and how much money you have to spend.