Well I've mined around planets that had two rings, inner metallic and outer rocky, and only the rocky ring had extraction sites, so I just dropped into the metallic one. Can't say I've done that much mining, but I've had two big sessions, one was dropping in, the other was at an extraction site, the only difference I noticed was more pirates in the designated extraction site.
I think the extraction sites are just a different place for hunting pirates next to nav beacons. I think the best place to mine is a random location at a pristine reserve metallic planet ring.
Does it matter whether you drop into a resource extraction zone or just randomly somewhere in the planetary rings. I swear I've had better finds inside the extraction zones but I don't know if it's just in my head. Plus those pesky pirates I'd like to avoid.
You can mine the rings of a planet?! How do you get to them without crashing?!