Skinning - Crit rating
Mining - Stamina
Herba - HoT (~2-3k@80?)
Alchemy - Arena potions. And 20% more effect from pots.
Blacksmith - BoP items. Extra meta gem or a weapon gem - depending on spec.
Tailor - Ranged root, BoP leg spell enchant. Flying carpet. Extra cloth drops.
Leatherworker - Drums, imba wrist enchant.
Engineer - BoP "enchants" - slowfall, rocketboots etc. The Hog.
Jewelcrafting - BoP gems.
Enchanting - BoP ring enchants.
Inscription - Extra major glyph slot.
Best? Don't think it matter really...
drums aint usable in arenas, dunno about tailor nets, but those too, probably, same with 90% of engi items.
also epic crafts are pve oriented, useless in anything past 1st midseason in LK
imo, it looks like alch will be the best arena prof with pots, than maybe herbalism with hot, maybe inscription for glyph, other than that, professions have only +stat boosters, which can be eventually replaced with gear/gems, so imo alch + ins/herb would be my choice for arenas