"Information Overload" - with today's technology we have access to do soooo much research! It drives me crazy sometimes. But, back to your question. I have recently been doing a bit of reading about thread. I recently read on Superior Threads website that you should piece with cotton thread to match the fibers of the fabric. And it is fine to to the quilting with polyester thread. I am sure you could find tons more on their website.
I have no experience with top thread, bottom thread, thicknessess, etc. But, with that said, I have been quilting for years and I have always used Coats and Clark Dual Duty thread for everything and have had no problems. I will be experimenting with new thread types...just for fun...or to make me crazy. Since discovering this board, I have been doing tons of research about a wide variety of topics. There are so many people here with a wealth of info. and I have learned a lot.
I think you will find conflicting information no matter who you ask. It is great to learn and be informed, but try not to let it paralyze you (that happens to me sometimes when I can't decide what advice to take!). Try to narrow it down, make you decision, and then start sewing!
I look forward to the responses in this topic.