Through traditional botting means, it would likely be fastest through mining/herb. However, this has greatly slowed down as of late as Cata comes to an end. Ore/herb prices have plummeted on most servers. You would make more if you could mine/herb it, then you had a Ench/jc/alchy to then shuffle it. That would maximize profit.
Edit: If you can't do the shuffle, then something to keep in my is this: Elementium Ore is going to keep on losing value as the MoP nears. It's almost exclusively used for the shuffle. As the enchanting and jewelcrafting markets crash (like they always do before xp's), Elementium ore is going to drop accordingly. It's already happening as I said. So it might be smart to switch over to Obsidium Ore profiles at some point. Obsidium Ore should maintain demand since it is used to level professions. Leveling guides avoid elementium mostly but they love to use lots of obsidium. So these profession levelers could be your next target audience instead of the current ore shufflers. Server prices obviously vary, but I've already noticed on my sever how Obsidium is now much more consistently going for more than elementium. You won't be able to deal out quite the volume you do with elementium though so be careful not to flood the market.