In reference to raiders - It seems to me that most people stick to one primary spec, and their secondary spec is used for their own personal amusement. In my case however, I actively maintain two roles and use both of those roles in progression (example - I was DPS on our Durmu kill, Tank on our Iron Qon and Twin consorts kills). So, I am curious as to what people in a similar situation use for their preferred professions - Or if you were in that role which professions you would choose.
For Reference, a list of the bonuses by profession (Special thanks to Rackfu for the list):
Jewelcrafting: Can use 2 Serpent's Eye Gems. Compared to using blue level gems, that is a bonus of +320 Agi/Str/Int or +480 Stam or +320 Spirit or some other combos which could possibly be better for some specs.
Blacksmithing: Socket Bracers and Gloves. Two additional sockets with a potential gain of +320 Agi/Str/Int or +480 Stam or +640 Spirit and some other combos which could possibly be better for some specs.
Tailoring: Cloak Embroidery: +2000 Int, +3000 Spirit or +4000 Attack Power for 15 secs on approx. 1 min cooldown. Averages out to about +500 Int, +750 Spirit and +1000 Attack Power... There already is a +180 Int Enchant and they cannot both be use, so this would give a average bonus of +320 Int. Does not appear to be a spirit cloak enchant and there are other dps (crit and hit)
Engineering: Synapse Springs or Phase Fingers. +1920 Agi/Str/Int for 10 secs/Min.... Averages out to +320 and could even be better if used with other cooldowns or during burn phases. I dont tank, but on use dodge bonus sounds helpful. Also a tinker for gloves to launch fireworks that do damage but sounds weak compare to synapse springs. No spirit bonus and since spirit is being made more important for healers, not sure if engineering is the best for them.
Leatherworking: Fur Lining Bracer Enchants... +500 Agi/Str/Int and +750 Stam... Compared to other available bracer enchants that is a bonus of +330 Agi/Str/Int and +750 stam.. There is a no stamina bracer enchant but there is a dodge bracer enchant so you have to compare dodge vs stam for that one.
Enchanting: Enchant Rings +320Agi/Int/Str/Stam. No spirit enchant for ring and stam is same as other stats.
Inscription: Secret Shoulder Enchant: +520 Agi/Str/Int or +750 Stam.... +320 Agi/Str/Int or +450 Stam compared to shoulder enchants available to everyone else.
Alchemy: Mixology (gives you more stats when under effect of a flask)
Skinning: Master of Anatomy: +480 Crit
Herbalism: Lifebloom: +2880 Haste for 20 secs. 2 min CD. Avg: +480 Haste
Mining: Toughness: +480 Stamina
I myself have chosen to use Jewelcrafting and Blacksmithing. My primary reasoning is the versatility it provides. When I am blood, I can stack mastery into the BS Sockets, and even use the JC gems for mastery. While frost I can stack strength or haste depending on what works best at the time.
I have a second Death Knight that I maintain as well - his professions are Enchanting and Mining. The reasoning behind that is - While Blood, I would have an extra double stamina (so I wouldn't need a stamina trinket). While frost I will have some extra survivability (since my gear will never be on par with my main), and extra strength. While it doesn't maintain the versatility - the raw DPS lost is not overly significant.
I was also frost/unholy, double DPS. I've recently switched back to unholy/blood because there are very few fights in normal ToT (and even fewer on heroic... which we'll be progressing on shortly) where frost is definitely "better".
Originally I went with jewelcrafting/alchemy because it was quick and cheap to level (think I did both the first few days of MoP for a combined total of 5k gold, from the AH) but now I'm running with Engineering/Blacksmithing.
Main reasons are:
1.) Engineering's just awesome. From a pure DPS PoV having a burst of strength every minute that can line up with things like disease application is great. If you really wanted to you could also add the frag belt for a bit of extra damage, I hear it hits for about 50k? I use the nitro-boost though, brilliant for things like getting out of the wind storm on Iron Qon (not so good when it backfires... never mind!). You also get fun little items like the goblin glider, Megaera trash? SKIPPED! (joke, wouldn't do that to my raid<3). Synapse springs also line up perfectly with Pillar of Frost if you're frost. The dodge bonus on demand is pretty good too.
2.) Unlike alchemy (which I had before) I get the 320str benefit from Blackmsithing without having to use a flask when I'm just doing dungeons, LFR or daily quests... Pop visions of insanity (as a cheap flask) and still have my profession bonus! Shove some mastery gems in there and you're sorted for tanking.
I started this xpac alchemy/engi and it was good, alchemy was good when I was selling engi mounts 100k a piece, and still had the bonuses were still there, also I am noticing now how much I miss 2 hr flasks ><. However I recently switched to enchanting over alchemy, cuz 1. static 320 str on rings is better than trying to remember to pop my flask, plus you can still use a elixir or something if you got it and 2. economically running old lfrs for VP and rolling coins have netted me lost of g as of late from sha crystals, and other than the time spent it is all profit unlike alchemy when u are spending mats for a chance at a possible big profit in living steel procs.
don't forget, come whatever patch they release epic gems on, BS becomes top and JC drops down below the rest.
Historically speaking they have upgraded the JC only gems to compete with the others - albeit later than necessary. On a more personal note, I would be perfectly content with blizzard not releasing epic gems at all - or putting a limitation on them and making them more difficult to acquire.