I think any cotton thread is fine, whatever your machine likes is usually my rule. I always use cotton thread for piecing and quilting anything that will be washed and dried so the thread will shrink along with the fabric. If it's a wall hanging that won't be laundered, rayons and poly are great. If you look at JoAnn's, even WalMart, they have cotton threads that are great for piecing. For color, if I'm using white fabric, I use white; otherwise a muted color of the main fabric color or grey.