Haste

Honestly this enchant is under budget in my opinion. Compare it to the Precision enchant and then look at what rare gems give you (Precise Scarlet Ruby and Rigid Autumn Glow). Sure below the dodge-cap of expertise it's value is higher than Hit, but Hit has the added benefit of working with abilities that behave like spells (namely Taunt). So my advice is take the Hit enchant and gem for Expertise if you need more threat. Don't waste the stat budget.

To clarify OneFreeMan's post, it takes 26 Expertise skill (or 214 Expertise Rating) to overcome bosses' 6.5% chance to dodge your attacks. According to this post on tankingtips.com, Expertise is so much better than Hit that the additional 5 hit rating offered by the Precision enchant still doesn't make it better than this one. I think for tanks, it's between this and Heavy Borean Armor Kit for your gloves. edit: If y

0.46% reduction dodge and parry at 80.
I consider this the best+threat enchant for blue geared tanks.
See also: This enchant