If you guys are interested. This guy did a VERY interesting comparison of virtually all the sound deadeners
available in 2002 or 2003. He then did a followup in 2005.
He explains how and why different deadeners work. What they are maid of, and how to apply them.
Keep in mind this information is almost 4 years old. There may be more recent information out there, but I've not seen it.
The link to his findings is below.