I use YLI 100 wt thread in neutral colors. I use a sort of khaki color for most things, white on white fabric, and off white for everything else. I've been using Thread Heaven and haven't had trouble with it fraying or making knots since then. It's a little hard to get used to since sewing with it is like sewing with a strand of hair, but after the quilt is washed, the stitches are totally invisible. I've found it a little hard to find around here and I've asked the local quilt shop multiple times to stock it, but they won't. The other day I found a website that has big spools of it, roserushbrooke.com, and I was pleased with their service. Connecting Threads also has it.