I've tried all of those stated in the title of this thread, plus sonic barrier.
i've settled on two small "blobs" of polyfill behind each midrange driver in the rear of each. In this particular situation, egg crate foam seemed to be more of a nuisance as it never wanted to stay in its place...
I use a combination of thick egg crate foam and polyfill for my sealed sub. It took quite a while to get a result that sounded "subjectively" better than just using one or the other.
My advice would be to stay away from the fiber glass if you dont like working with it...polyfill will do the same job(at a higher cost).
Experiment a little...
