I am learning about batting (among other techniques!) Can anyone give a thought about when to use which kind of batting?

I learn that the thinnest batting is good for FMQ'ing,(I meander and STID) and in using/doing that... I find the quilt to be stiff which is fine if used as a blanket. However, I want a quilt for a child to be soft and cuddly. Even for me.. I have one that I meandered to use at the TV to cover with (when it was cold) and it was so stiff... I couldn't get it to "form" around me enough to stay warm and finally just went back to my crochets afghan for great warmth! So I want a quilt that will be soft, cuddly and "wrap-up-able".

So..I recently heard something about the thickness of the batting..thinner it is, stiffer it will make the quilt.THe close the FMQ'ing, the stiffer the quilt. However, I have heard that the thicker/puffier the batting, the harder it is to FMQ and (from experience) the puffier the quilt, it tends to just look kind of sloppily made.

So can I hear what y'all think about batting and how you use the different thickness's of batting? And what kind of difference is there between cotton and polyester batting