I presume these are sealed boxes. In that case, you usually want an even distribution of the stuffing throughout interior volume, so batting is probably not ideal. Batting is better for vented boxes when you want to keep the stuffing in place - specifically, away from the port openings.
I prefer Poly-Fill from Jo Ann Fabric, etc, over Acousts-Stuf for sealed boxes. It has finer-diameter fibers, which is desirable in my opinion. It also retains its loft better than cheaper brands.
In practice, the exact stuffing material you use probably won't make an audible difference in a subwoofer's performance.
Duke