your thread choices are as individual as your fabric choices. i peice with cotton, poly, wool and silk thread...just depends on the project. my favorites to piece with are poly (stronger, doesn't tangle as bad as cotton) and silk (my favorite for hand piecing) but i seldom worry about it...as long as the thread is strong enough to hold up and the right color i use it. as for weight i usually use 50 weight, except the silks are 100 wt. (very thin) great for applique.