I sew with cotton, poly wrapped cotton and poly, depending on the color thread I need. I quilt with cotton and poly - usually cotton (King Tut) on top and poly (Bottom Line) in the bobbin. Sometimes I use poly (So Fine or Bottom Line) on top as well. Superior Threads has a great deal of information on their website about thread. Just go to
http://www.superiorthreads.com/ and click on the "Education" tab...SO much great information from someone who lives and breathes thread!