My own superficial impression (without doing any valid measured comparisons) is that the eggcrate foam doesn't absorb very much sound, the home insulation seems to do a good job but is too thick for some appliciations, especially in small volume enclosures, and the 5/8" rigid fiberglass seems to be the most effective. I have used all three, but when I have completed an enclosure I'm not inclined to remove and reinstall damping material (especially the rigid Armstrong ceiling stuff) through the driver holes, so I haven't done any valid comparisons.

Wayne, Bob, others, what do you think?