I use 50 wt for machine piecing and applique, 40 wt for hand piecing and machine quilting. I usually machine piece with Gutermann, but have tried Superior Threads Masterpiece, which I really liked. I tried Presencia 50 wt. for piecing, but it seemed unnecessarily thick to me (but very strong). I use Superior Threads King Tut for machine quilting. I've only used Aurifil so far for hand applique. All of the threads above are 100% cotton. It's a personal preference if you want to use cotton or poly. Lots of people rave about poly threads for machine quilting.