The main difference among threads is fiber content (rayon -- great sheen, but weak, used mostly for decorative stitching), cotton (people used to think it wouldn't tear fabric if there was stress on the seam, but that's not a realistic problem from my point of view as someone who taught classes about fibers, and it does create lint, is often thicker than poly), and polyester (strong, thin with little lint). There are also cotton/poly blends that have the strength of a polyester core and appeal of a cotton cover. I think they just add lint and thickness. Over the years I've switched from cottton to Glide polyester. You could get spools of other good brands and see which you and your machine like.