I use different threads because I have a lot of different threads. Right now I'm using InvisFil thread top and bobbin. I buy a spool of different brand thread at every quilt shop or show I visit. It doesn't matter to me if it is poly or cotton. Most of the best threads for machine quilting are poly. YLI silk thread is the best thread I have ever used but way too expensive for everyday use. So far I'm finding that InvisFil thread is very close to sewing with silk thread. I use a lot of Connecting Thread's brand.