I'll be watching this thread to learn about threads. LOL.
As someone who is new to the sewing craft, the only difference that I can tell between threads is how linty they are. I've been using my JoAnn coupons to stock up on their Guttermann 50wt cotton thread, I think it is my favorite for piecing, and I don't see much lint using it. For quilting, I've been using Sulky invisible thread and like it.