I have had great luck with Superior Magnifico.. Great fill. The only problem for me is that it doesnt come on mini cones so its hard to have many colors. But I bought the ones I will use the most. My next thread of choice is Isacord. These are both 40 wt. the bobbin thread needs to be thinner than the top. I use 60 wt. Bottom Line works good for my bobbins.