The NM's (like the Company Sword Antican) drop the ore more often, friend of mine got 7 ores in one night camping the NM. Mining the ore is pretty slow and depending where, you've got RMT competition. You can find Darksteel in Zerhun(very rare result), Gusgen (a little better result but RMT plague inside), Yughott (very rare, sorta like Zerhun), the 2 Movapolos (not sure how hard to mine but mining spots are far apart and w/o map, pretty annoying)...and every miner's favorite, Ifrit's Cauldron, but we all know what can go wrong there.