As of 5.0.5, all the 170 primary stat bracer enchants are +180 (the spellbook enchant tooltip does not reflect this, but the on-item tooltip does), so leatherworking no longer has that slight advantage.
But Blacksmithing undoubtedly has the most flexibility and is the wisest choice in looking towards the future when MoP epic gems come out. In Wrath, they buffed JC gems accordingly to match the increase in epic gems. In Cata, they did not. Either way, Blacksmithing's perk will increase from epic gems. The other professions probably won't.