Well why not choose the option which is the most profitable? This means you will need to look at your AH. You will also need to tic what will sell as well as how much profit there might be. We gave no idea about the prices on your server or the demand. If you have a ton then try all 3 and see what works.
All Pandaland enchant mats (dust, essences, shards) are dirt-cheap on my server, the scrolls as well. Basically to turn a profit you need to AH-search which enchants are flooded (all MOP weapon enchants are undercut severely on my server) or not. Supply and demand.
Or you go after pre-MOP enchanting dust and sell. Those sell really well and very expensive to boot. Good ol' twink enchants are also very profitable, like Crusader.
If your server is med pop + and you are on the most populated faction, the price between the two will already be very close on AH to the point where the sole goal of upgrading dust into essence is so that you can sell on both front and thus sell more. Most non-enchanters buying mats still don't think they can just upgrade so they'll buy exact mats per say.