Just want to comment on the materials. I have neither, and don't think one can fairly "vote" on the only one they have, unless they've had both.
The "dyneema blah blah, grid this that" materials both packs use are *very* similar, likely milled at the same plant. Yes the burn uses a heavier fabric. All of these materials of similar make I've worked with have tendencies to fail first at the coating and then later in the weave. Honestly, I've been curious for a while why neither of these companies have embraced the superior laminates offered by Dimension Polyant. Or the cuben hybrid HMG uses.
As far as the mesh however, the GG "power stretch" type mesh is *extremely* durable in my experience(used a gorilla for a couple years, and made a number of packs and accessories using the same mesh personally), and the best stretch type mesh I've ever used. It's a strangely tight knit with good abrasion resistance, snag resistance, stretch, and body. I personally like it much better than the stuff MLD uses, which offers no stretch, and I've found snag prone, but I'm not trying to disparage their quality or workmanship in anyway, which is admittedly, excellent.
I guess all I'm trying to say is, if you're trying to make an argument for durability or material quality on either of these packs, it is, in my opinion, a superficial one.
The hip belt argument may be a valid one, based on personal preference. Personally, in SUL loads that these packs are designed for, I don't like or use a hip belt personally. I'd rather cut a webbing one off, and the Burn's belt is *barely* more than webbing. On the flip side, I prefer the burn's full mesh back and side pockets, which offer more *real* storage. The GG pack sacrifices function in favor of form in those areas IMHO.
Would be curious to hear some first hand experience from anybody that's had both and favors one over the other for other reasons than individual "fit" type reasons, that is, if any such person exists. ;)