There's been talk about pink fluffy (not dense) vs rigid boards and how well they work at different thicknesses with and without air gap.
From what I gather, exact gas flow resistivity numbers are hard to come by partly because of sample variation and testing methods.
Anyway here are some resources to help get us started. Presently I'm building superchunks out of Johns Manfield R19. According to the chart below, which may not be 100% accurate, it's resistivity is 1674 rayls or whatever. Rigid board will generally fall in line with the second, linear chart. You can then plug those numbers into the Acoustic Modelling calculator and see what kind of absorption coefficient you get.
Holy heck this is old. Yes, they're working out grandly. Rigid is probably better but more expensive. Just make sure you cover the insulation, if you plan to build them with fluffy, because I didn't and that stuff gets on everything.
I'm not sure super chunks are better than a rectangular trap other than conserving floor space and money. 2' fluffy and 8" of rigid is all you need at any given location to treat down to 63Hz.
If I could go back and start from scratch, I'd probably just buy 3x as much rigid as I did and put 8" panels everywhere. However, living in apartments, not all the ceilings are good for hanging heavy things. Even so, a bunch of free-standing 8" panels is probably the best in addition to whatever you put on the ceiling and diffusion. That being said, I haven't compared super chunks to thick panels so this is sort of just conjecture.
TL;DR - Super chunks are good but perhaps a greater quantity of overall absorption is better.