My service tech lady who is a Pfaff expert gave me the tip that the 80/12 works best with my Pfaff. I found this to be true after I decided to take notice. I also use the Topstitching or Microtex varieties. I continue to use the 80/12 with quilting as it is still the one that works best. I use Aurifil or So Fine thread.
Please note this is the quirkiness of my Pfaff.