The thing is, economies can vary from server to server, as well as from day to day. Your best bet is to see what sells on your server, and maybe take a week or two and mopnitor different ores and herbs. Maybe take your herber & miner out and see which can get the most mats from different areas. Note what sells, and how easy it is to get. Sometimes the item that sells for the most gold (for example, titanium) is not easy to find, and thus will not net as much profit as something that sells for less per stack, but is easier to farm (saronite or cobalt). I personally prefer mining, but that's because I have a jewelcrafter and an engineer. The money I make from mats from either mining or herbing often sells for more than crafted goods I could make with them.
Also, bear in mind things may change from day to day, even on one server. If the raiding guilds on your server all raid on a Tuesday after maintenence, you may sell potions for profit on those evenings. You may find that crafter things sell better on a Friday night, when the "weekend warriors" run to the AH to gear up their characters. You may find that potions and other crafted items (like weapons & armor) sell for less than the cost of the materials, since people may be leveling their craft and trying to offload surplus.
Thus, I would suggest that only you can really determine what will be better, and only with a little effort in watching your realm's economy.