If you look at soundproofing materials, such as the egg carton foam they put in recording studios, and sound-absorbing panels they put in auditoriums and restaurants, you will see that they are very textured with lots of nooks and crannies. Based on this observation, I would use a lofty batting.
Honestly, if I were trying to dampen noise in a room, not only would I use wallhangings (multiple, if possible) I would also hang thick draperies such as velvet or velour, and even investigate adding something to the ceiling.