I used bobbin thread years ago when I had an applique business. It was cheaper than the top thread we were using to match the applique and since we were doing lots and lots of applique it made sense to save where we could. I probably still have a couple of spools tucked away somewhere. Now I use Aurifil both top and bottom when piecing and if I'm going to need a particular color because it will show I look in my stash first and use that up. For the most part it's Guetermann but I also have some C&C Dual Duty because the store that is closest to me sells that and not the other. I do love Aurifil but beyond that I don't care as I don't think it makes much of a difference.