I have used both cotton and poly for my projects. I prefer cotton, but if I need something sturdy I use poly, depends on the project and what I am sewing. As for brands I have used many, gutterman, mettler, connecting threads, sulky, coats and clarks, and all have done well. I use gutterman the most for piecing because of sales and coupons for joanns. My machine isn't picky, but some are so I say use what your machine likes, you do not have to go out and buy expensive thread. Some will suggest it but completely uneccessary. I really like mettler but it is expensive so don't use it much. I like the look of sulky's quilting cottons but haven't used them but for practice and have no other brands to compare. Cotton in very linty compared with polyester, but I always clean out my machine after I am done sewing so I have never had a problem. If we are talking embroidery than that is a whole other subject of thread