I use a lot of thread for many different things, including when I'm doing my embroidery. My machine loves it all so I use it all when I find what I like. When it comes to piecing, especially if you are dealing with a block with lots of small pieces I only use Aurifil. It's two ply and my blocks come out the right size. Most threads are 3 ply and you can believe how much one ply extra will make in your quilt size. Plus I only use cotton for piecing on cotton fabric so that it'll have a better chance of lasting as long as my fabric does. Other threads, poly, rayon has a tendancy to cut thru cotton over time so I don't take a chance even though I'll probably not be around in the time it takes to happen but I want my quilts to last way after I'm gone.