When I was using my friend's long arm, we were getting our best results from So Fine prewound bobbins and I became a fan. Then I won an auction thing for a huge lot of Sew Fine cones. I use it almost all the time now for my bobbin thread, piecing and quilting. I've also been using it for domestic quilting, or at least when Cranky Bernie (the bernina) was working, it like So Fine and Aurifil threads.
https://www.superiorthreads.com/thre...ne-50/c/60-205