Reframe the question.
What "quality" are we talking about?
There is no single component that makes for a briar's "quality".
Resistance to burnout is probably inverse to ability to sandblast deeply. Grain density is usually related to actual physical density, so if you want really tight stripes, maybe you can't have a super light pipe.
See what I'm saying? There's no one thing.
I pay more for blocks with higher grain density. Ordinarily these have higher ring density (ie they are slower growing) and that makes for difficult sandblasting.
But if we are just talking about smoking characteristics... well, again, do you want something ultra dry and a little earthy, or something with a little bready sweetness? Do you want wood that carries the heat outward to "cool" the smoke as it were, or do you want wood that acts like an insulator, allowing your burn to remain at an ultra low temperature? Even if, even IF I could give you a piece of briar that did all the things you think the ideal piece of briar should do, the next guy might not agree.