I generally use Mettler or Aurifil thread for piecing and some machine quilting. I like Coats and Clarks poly for the vast array of colors that work well for machine quilting on my domestic machine. I prefer silk thread for applique, and my Joann's only sells Guterman so that's what I use. I really think what you use depends on what you're doing with it, and on your machine. Some are finicky!