I continue to try to figure out crit immunity. There's just too many options out there: gear, enchants, gems, potions. To help myself sort them out, I've made a little spreadsheet analyzing the tank points costs for the gems and enchants. Take a look!
My conclusion is of the various gem and enchant options, the two best tradeoffs are Enchant Bracer - Major Defense and the new Enchant Chest - Defense. The new Steelweave enchant for cloaks is not as appealing as I'd hoped.
The spreadsheet calculates the tank points for various gem and enchantment slots using Emmerald's high gear tank points calculation. It then compares the cost of using a crit immunity item vs. the best avialable item. For instance, Bears have two good choices for enchanting their cloak: +12 Agility or Steelweave for +12 Defense Rating. The agility enchant gives 0.82% avoidance and is worth 79 tank points, Steelweave gives 0.4% avoidance and is worth 36. So you lose 43 tank points to get the extra 12 defense rating from Steelweave. Is that a good tradeoff? Maybe. But you should probably look to the Chest enchant first because it only costs you 20 tank points for 15 defense rating. The bracers enchant is 15 tank points for 12 defense rating.
My spreadsheet analyzes all of the gem and enchant options that give you crit immunity and boils down their value in the %26quot;cost%26quot; column. Bracer and Chest enchants are best. Beyond that gems and steelweave are all roughly equally good tradeoffs. What I don't have on that spreadsheet is the value of changing out your gear. For the T5ish stuff I own downgrading my gear for defense is generally the worst option, although these PvP boots are a very pleasant exception.
Update: there's some discussion on my spreadsheet on Emmerald's forum.