Best Professions for Warlocks

Every since the release of World of Warcraft, you can select only 2 primary professions in addition to having all three secondary professions of fishing, cooking, and first aid. So what 2 professions would be best for your DPS?
Let look at the list of available professions. In all of the calculations below, I will use my personal spec and gear as the basis. This is tuned for high-end raiding destruction warlocks (destruction warlocks are proably 90% of the raiding warlocks out there). The following values will be used in the evaluation because they are my current Leulier spreadsheet DPS values:
+1 stamina = +0 DPS
+1 intellect = +0.20 DPS
+1 spirit = +0.11 DPS
+1 spell damage = +1.10 DPS
+1 spell hit = +1.78 DPS
+1 spell crit = +0.84 DPS
+1 spell haste = +1.11 DPS
+1 MP5 = +0.30 DPS
All spell hit ratings will be ignored becuase it should be easy enough to reach the spell hit cap through other gear and/or gems.
Skinning, Herbalism, and Mining:
These three gathering professions do not give any added benefit to your DPS. While it can be said that having a profession like herbalism will give you easier access to herbs for your alchemy, the same can be said for using gold to buy them off the Auction House. The only item in the game that requires Herbalism is [Fel Blossom], which is pretty useless since it shares a cooldown times with a [Master Healthstone].
Mining and Skinning are equally useless, and have nothing that is profession specific for them. Along with Herbalism, everything these three professions gather can be obtained from your alts, friends, or the Auction House. It is true that some raids needs a miner in certain instances, but let someone else who is not DPS focused like you are have that job.
Alchemy
A warlock can benefit from the Alchemy profession by wearing a [Sorcerer's Alchemist Stone] in a trinket slot. This is a relatively new trinket as it was added in Patch 2.4.0, and it requires being exalted with the Shattered Sun Offensive.
To evaluate the DPS of this trinket, we will have to assume we are chaining [Super Mana Potions] and determine how much of a benefit the 40% potion boost would be. We will also have to consider any DPS loss (if any) from not wearing a better trinket in that slot.
An average Super Mana Potion will restore 2400 mana and can be taken every 2 minutes. To convert this to overall MP5, we can do the math to determine that using Super Mana Potions gives an equivalent 100 mp5. However, with this trinket, the 100 MP5 becomes 140 MP5, so the benefit this trinket gives is +63 spell damage and +40 MP5. Now let's turn to our Leulier spreadsheet that tells us our DPS values for each point in these area. Using my Leulier values above, I receive a DPS boost of 81 DPS.
Now let's compare this to several other trinkets you might have put in the slot.
[Shifting Naaru Sliver]: 119 DPS
[Hex Shrunken Head]: 97 DPS
[The Skull of Gul'dan]: 93 DPS
[Darkmoon Card: Crusade]: 87 DPS
[Sorcerer's Alchemist Stone]: 81 DPS
[Sextant of Unstable Currents]: 78 DPS
[Icon of the Silver Crescent]: 76 DPS
As you can see, the alchemy trinket would not be the fifth best trinket in the game. So while this trinket might be easily obtainable and also uber for a lock just starting out, eventually for end-game raiding you will want to replace it. Getting the maximum DPS out of this trinket also requires you to be chaining Super Mana Potions which constricts your potion options.
Blacksmithing
There is no gear or consumable that can be used by a warlock.
Enchanting
The enchanter's only DPS increase is their ability to enchant their own two rings with Enchant Ring - Spellpower. This results in a total of +24 spell damage for 26.4 DPS. Only enchanters are able to enchant their rings. It must also be noted that you can drop enchanting after you enchant your rings and still keep the enchants! This seems to be almost a loophole of sorts, but it works.
Engineering
The engineering profession gives some very interesting gear choices for warlocks in all level of raiding; generally speaking Engineering provide profession specific head pieses. For end-game raiding, there is the [Schematic: Annihilator Holo-Gogs] that is a rare drop from Sunwell trash. Let's compare this helm to other end-game raiding helms; the DPS values below consider sockets, and the socket bonus, but not the meta gem itself.
Each of the alternatives has a meta gem socket, so they are equal in that respect. The Dark Conjuror's Collar and the Helm of Arcane Purity comes from Kil'jaeden, the very last boss in Sunwell Plateau. Therefore, we will not compar our engineering helm to those two pieces becasue you should really select gear based on what will help you kill the "last boss". So we will compare the engineering helm to the Cowl of the Illidari High Lord; therefore the engineering helm whould be counted as a 16 DPS increase while understandthing that there is a much better helm that drops from Kil'jaeden. There are of course other fun things that come with being an engineer, but they do not increase your DPS in end-game raiding.
Jewelcrafting
Jewelcrafting is another interesting option for end-game raiding. Basically, jewelcrafting will allow you to cut better epic gems that are BOP. Jewelcrafters are also able to craft profession specific neck pieces that are BOP. Again, there is a trash drop in Sunwell Plateau of the [Design: Pendant of Sunfire]. Once again we will compare this neck piece to other end-game raiding pieces.
It is very interesting to note that the #3 DPS neck piece in the game is from the honor PVP rewards. The #2 necklace is a drop from The Eredar Twins in Sunwell Plateau.
There are also two Unique-Equipped BOP gems that a jewelcrafter can cut. These are [Don Julio's Heart] for 15.40 DPS and the [Blood of Amber] for 10.08 DPS. The blood of Amber is less DPS than other epic gems, so we will disregard that gem. This leaves [Don Julio's Heart] to be compared to a [Runed Crimson Spinel] at 13.20 DPS.
Therefore, the DPS increase for the jewelcrafting profession is (103-82) + (15.40-13.20), which is 23.20 DPS.
Leatherworking
Leatherworking has taken on a life of its own for end-game raiding guilds; all because of this little consumable called [Drums of Battle]. It's not a trinket, so it doesn't take the place of any gear. It does use a global cooldown, but since your trinket does not, you can put it in a macro to use it at the same time as a trinket to combine their effects. This little item of uberness gives 80 haste (spell, melee, and ranged haste) not only to you, but your entire party for 30 seconds. For the purposes of any on-use item or trinket, we convert this to overall use by diving the buff over its cooldown. So this is equal to a 20 spell haste bonus for you. Using our Leulier spreadsheet, this provides a 22.2 DPS increase just for you. This would probably be fine if it stopped there, but it doesn't. Since it effects everyone in your party, the effect must be multiplied for your party members; let's assume:
You, warlock of uberness: 100% of your DPS
Another warlock, almost as good: 95% of your DPS
Shadow Priest: 58% of your DPS
Elemental Shaman: 80% of your DPS
Mage: 83% of your DPS
Doing this math results in a
raid DPS increase of 92 DPS. This value is for 1 set of drums in the party. More party members that are also leatherworkers would be able to chain-use these Drums for an additional 92 raid DPS increase.
Tailoring
Almost every raiding warlock started out as a Shadoweave Tailor when TBC expansion was released because of the three Frozen Shadoweave pieces, for good reason too. Those pieces gave a huge head start when everyone started out raiding Karazahan. However, as they progressed, people eventually replaced all three of those pieces with better gear around the T5 level. There is one item left in the end-game that may breathe new life back into Tailoring. It is the [Pattern: Sunfire Robe] that drops off of trash in Sunwell Plateau. Let's compare this to other end-game chest pieces.
It should be noted that the #2 and #3 items are extremely similar, and it is surprising even that they drop from the same boss in Sunwell, M'uru/Entropius. Given the different socket colors, for us at least the DPS for either item becomes indistinguishable.
So overall the tailoring profession will give you a 24 DPS increase over other Sunwell loot.
Conclusions
Sorting the results of the above, we find that:
Leatherworking: +92 raid DPS (but only +22.8 DPS for you)
Enchanting: +26 DPS
Tailoring: +24 DPS
Jewelcrafting: +23 DPS
Engineering: +16 DPS
Alchemy: A help for new locks, but there are other trinkets that are better and easily obtainable.
Blacksmithing, Herbalism, Mining, & Skinning: No DPS increase
Since the benefits of the Leatherworking profession go beyond just you and the raid DPS increase is significant. Therefore, the first choice profession for warlocks must be declared as Leatherworking.
The second choice profession is Enchanting; however, as we discussed previously you can enchant your rings and drop the profession to pickup another. So the strategy here is to level enchanting and get your final two PVE rings of choice, enchant the rings, then drop the profession for something else. For me, my final two rings are the [Ring of Omnipotence] which drops from Mu'ru/Entropius and the [Ring of Ancient Knowledge] from Black Temple trash. For me these, two ring give me the highest DPS excluding the spell hit rating given from other rings (I plan to reach the spell hit cap from other items).
So after you enchant your final two rings, then you can pickup Jewelcrafting or Tailoring becasue the DPS increase for either items is practicially the same. I would recommend not droping enchanting for tailoring or jewelcrafting until after you receive one of the patterns. If you don't wait, then you basically have a profession that does absolutely nothing for you while you wait on a CHANCE at receiving a very, very rare trash drop from an instance you probably do not have on farm status.
I would not recommend the engineering profession since it is the lowest DPS increase of the exisitng sunwell profession drops.
Summary
In summary, what I recommend for end-game raiding warlocks to do:
1. Pickup Leatherworking and level it to 350. You can use [Drums of Battle], even though you can't craft them.
2. Pickup Enchanting and level it to 360. You can enchant all your rings as you get better rings. You can also enchant your two PVP rings and keep the enchant effect in arenas.
3. Wait until you can optain one of the trash profession patterns from either tailoring or jewelcrafting. You do not need the profession to simply receive the pattern/design. When you receive either item, drop enchanting and level up your new tailoring or jewelcrafting profession.
4.a. If you receive [Design: Pendant of Sunfire], then drop enchanting and pickup Jewelcrafting and level it to 365 for the neck and gem.
4.b. If you receive [Pattern: Sunfire Robe], then drop enchanting and pickup Tailoring and level it to 365 and craft your robe.
It might seem a lot of work to drop enchanting to level jewelcrafting or tailoring, and you would be correct. To each his own, and your mileage may vary. Feel free to leave any questions or comments!