Superior Threads does not carry Aurifil or Mettler
I use Aurifil 50wt cotton for machine piecing with Superior Threads' Bottom Line in the bobbin*
I use Mettler 60wt cotton embroidery thread for hand piecing.
* I buy their pre-wound bobbins (superBobs). The thread is so thin it doesn't matter what colour you use. I once pieced a twin top with 1 bobbin.