Done most of my post-BC mining in Nagrand. Has a bigger proportion of adamantite nodes than Hellfire does. Can be done pretty well without a flying mount, but there are lots of areas more easily accessible once you get that flyer.
I love Nagrand, it has fel iron, adamantite, rich adamantite, and still the occasional khorium. It also seems that nagrand has more spawn places then any other area. I got my epic flyer in about one week just grinding out Nagrand of all its ore.
I just came across rich adamantite for the first time this weekend. Previously I've not got more than 3 adamantite ores from a single vein and but yesterday I had two of these, with 6 ore each.
Nagrand is good, I have had some decent luck just while questing in netherstorm, found about 5 khorium veins and quite a few adamantite veins. Strictly for grinding ore though (without a flyer) nagrand is probably the best.