Well, do whatever works! If something is working for you, dontvlet anyone talk you out of it. That said, I use 50 wt cotton Aurifil or Masterpiece by Superior (also 50 wt cotton, but sometimes has the color I want, or I'm working on a machine such as a featherweight that "likes" as horizontally wound spool) to piece. I prefer thicker thread, 40, 28, or even 12 wt for most quilting. I only use 50 wt when I want it to blend in.