Edit: On 5.4 PTR, all professions are neutralized, and grant profession perks based on character level rather than profession skill point. If this change carries to live, then this thread will become obsolete.
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Since the title is still available in Mop, it is worth to mention a few things about choosing profession if you really want to save time for grinding a BiS set for this. Notice that the minimum required level to train 600 profession is 80, and in future expansion the minimum level would likely be increased to 85 (always 2 expansions behind), so it may be a good idea to start building an 'ultimate herald toon'.
Consumables:
Lv.80 toons can use cata flask such as Flask of the Draconic Mind, and cata food such as Fortune Cookie. MoP food and flasks requires Lv.85-Lv.90 to use.
Profession Bonuses:
Alchemy: Gain from this profession would be limited to 16 prime stats (24 if stamina, which has a 1.5 multiplier, same calculation below), no matter what level of flask you used. Also, it should be noted that Alchemist's Flask can be tricky. Although it states as a 320 prime stats boost on tooltip, when consumed by a Lv.80 toon, it only gives 16 stats boost (which is calculated based on WotLK flak stats).
Blacksmith: Even though wrist/glove socket does not have restriction on item level, the gems do, thus the bonus would be 40 of any stats.
Enchanting: mop ring enchant requires minimum ilvl of 372, thus we can only cata ring enchant, which is 80 prime stats.
Engineering: engineers have access to their latest perks such as Synapse Springs, which is equivalent to 320 prime stats. In addition, they also have quality of life bonuses such as Nitro Boosts, making engineering one of the most useful profession for this fight (dps and tank wise).
Herbalism: these herb farmers have access to Lifeblood, equivalent to 480 haste. Based on class and spec, this can be an insane burst. However, farm herbs on low level alt can be a painful process.
Inscription: the mop bop shoulder enchant requires lv.90 to use, thus they can only use cata inscription-only shoulder enchant. However, it should be noticed that normal shoulder enchant from therazane is not available to lv.80, which makes this profession slightly better than enchanting (roughly 100 prime stats).
Jewelcrafting: gems has item level requirements, thus the bonus would be 40 of any stats.
Leatherworking: Not only they have access to the latest wrist exclusive enchant, but also they can use the cheap leg enchant. For agi/str users or tanks, the bonus can reach as high as 750 prime stats, even for casters the bonus would be near 500 prime stats.
Mining: miners have access to Toughness which increases 480 stamina. Only useful to tank, and farm minerals on low level alt can be a painful process.
Skinning: skinners have access to Master of Anatomy which increases 480 crit. Though, farm skins on low level alt can be a painful process.
Tailoring: Not only they have access to the latest triggerable back enchant, but also they can use the cheap leg enchant. For casters or healers, the bonus can reach as high as 800 prime stats, even for agi/str dps, the bonus can reach 400 prime stats.
Conclusion:
Leatherworking and Tailoring are easy winners for most dps/healer, while herbalism/engineering can be useful for certain dps classes and mining can be useful for tank.
Last edited by bqiyue2 on 2013/07/05 (Patch 5.3.0)
KzanolNS on 2013/08/17 (Patch 5.3.0)
Just to mention, it REALLY is worth it to grind professions on your Herald toon. Don't worry about BiS gear, regular gems, enchants, focus on professions. On my hunter, on which I just did Herald today, I got 14k DPS with mostly JP purchased gear (no drops from Ulduar used at all) and 575+ engineering and leatherworking. It does pay off, so don't underestimate it if planning to do the achievement.
bakhtarrh on 2013/09/20 (Patch 5.4.0)
With patch 5.4 it is, unfortunately: Quite the contrary. Bqiyue2's apprehension came true: The professions are now tied to the player level. With level 80, it does not make any difference for you if you have Skinning at 450 or maxed out to 600: 48 crit is what you get. With Leatherworking it is the same: +50 on your wrist. I did not check the other professions, yet. I'd assume 1/10 for them, as well.