I use Aurifil cotton and cotton Masterpiece by Alex Anderson and polyester So Fine by John Flynn mostly. So Fine is so wonderfully great for piecing. I understand that Linda McCuen (sp?) used So Fine for quilting the $100,000 winning quilt "Bella" she did several years ago. Even professional quilters don't agree on what type to use, so experiment and see what YOU like. Just DON'T use those 10/$1 threads you find in discount stores. They are too inconsistent in the thickness and produce so much lint that they are TERRIBLE for your machine's tension discs. I can't tell you how many times a machine has come in for repairs in the shop I worked in, just to have it be the cheap thread that was causing the problem.