I prefer cotton batting but that's just what it is - a preference. One kind is not necessarily better than the other. If I'm making something that is more disposable than a quilt then I don't think the batting makes much difference. If I put a lot of work and money into piecing and quilting a quilt that is going to be used by people then I'm not going to scrimp on the batting. If I'm making place mats, wall hanging and such then I'm more likely to use a less expensive batting. I save all my scraps of batting and sew them together. I think it's harder to sew poly batting together. Cotton is very easy to piece so in the long run maybe I'm not spending that much more for batting because none goes to waste.
Relax, use your batting, improve your free motion skills in the process and have some fun.