I mostly use poly batts. I'd say that Dacron is a registered tradename and has some proprietary benefits in their processes but that it is fully poly.
I like the lighter weight and density of poly batts but I also prefer less quilting and puffier quilts than is currently popular. I feel poly batts are better for my allergies and my need to wash my bedding frequently.
There are also silk and wool batts, and bamboo or other fibers. Some people don't like the amount of processing/chemicals used in bamboo but some people like the weight and drape.