I was using Mettler because that was what I was told to use when I bought my machine. I had a spool of Coats and Clark on it when I went back for my guide class after I bought the machine and was told it was not good for Nina (the shop's pet name for all Bernina sewing machines) to use that. So I bought Mettler--but it's expensive. I recently order Connecting Threads and Nina seems to like it just fine. Been working on 2 quilts today with no problems at all.