I've used both. I prefer the 50 weight Machine Quilting Threads. My favorites are Aurifil and Wonderfil, I've used Coats & Clark Dual Duty, but it's usually cheaper to get a larger spool of Aurifil than a few smaller Coats & Clark spools. Guttermann works well for me too. I tried Connecting Threads thread, but my machine didn't like it.