I enjoyed the Iridium in Omicron Delta... Usually plenty of rowdy bounty hunters, passing corsairs and friendly zoners in the area.. as well as the Order Fleets passing through occasionally. All of that AND nomads attacks nearly blasting you and your freshly mined Iridium to pieces from time to time. It isn't peaceful, but it has entertaining qualities.
But to each his own, I have yet to explore other mining opportunities really.
*edit* ah almost forgot to mention, Iridium seemed somewhat slow, I never really seemed to get more than 10 rocks at once so... average of 4 or 5.
I always start mining gold in the dublin system. Corsairs show up to rob you, but you just thrust to the nearby Bretonian battleship and it will get rid of them for you. Then you can go back to mining.
I stay at pittsburgh these days, seems the niobium mining in O49 has been adjusted down alot.
599 for each scrap, the base is close to sell at and scrap fills up in your cargo hold pretty fast (alot yeild compared to other stuff)