I have great results with Aurifil cotton 50wt, and I always have pieces of it leftover from rethreading my machine (since one is supposed to clip it at the spool and pull it through the needle). I also use Masterpiece by Superior. They have two sets of about 36 bobbins of every color they make. I also love 100 wt silk thread by YLI, but I don't have as many colors of that, so I mostly use it for light, neutral backgrounds.