can't add anything new, really. I go with neutrals, and I use Essential threads, 100% cotton.
I have read, that the caution about cotton thread to cotton material, is not as much a problem, now that ppl do machine quilting. It was very important when most were hand quilting. I am a little on the cautious side, and as i gain experiece, i may branch out later. For now, have much cotton thread, as I stocked up! :D
P.S. not to confuse you...you will learn in time, their are many opinions on many things, in quilting, that is why you hear the refrain...whatever YOU like or want...there are some professional quilters, that press their seams open. They say...lol, ('they say") that their seams lie flatter.
I will probably do some of both. :D