when I use poly I always use a lower loft--even though I sometimes double that. Poly is good for quilts that will get washed often, need some puffiness to hi-light the quilting,or a quilt that you plan to fold or mail as the poly does not hold onto the fold creases as much as cotton--so a show quilt may have poly. What I don't like about poly is it doesn't breath and holds in the the moisture . What type of quilting is limited by your skill level--if you haven't done a lot of FMQ then I'd definitely suggest you use low loft as less chance of puckers.