A quick glance at the benefits and downsides of reaching crit immunity via Defense versus reaching crit immunity via Resilience for Bear tanks.
Any level 70 player with their normal Defense skill maxed out at 350 has a 5.6% chance of being critically hit by a level 73 mob, a.k.a. raid bosses. This comes from every mob having a base 5% chance to crit a same-level opponent, plus the increase in crit chance due to the difference between the attacker's weapon skill (365 at level 73) and the target's defense skill (350 with no bonus Defense from gear or talents).
Feral druids, by putting 3 points in Survival of the Fittest, get a free 3% crit reduction. That leaves a 2.6% crit chance that needs to be eliminated with gear.
There are two stats in the game that reduce a player's chace to be crit; Defense and Resilience.
Defense reduces a player's chance to be crit by physical attacks by 0.04% for every point of Defense Skill (not to be confused with, but rather a product of Defense Rating). Every point of Defense Skill also increases a player's chance to be missed, to dodge, parry and block by 0.04% each. Druids lack the ability to parry and block, so in addition to the crit reduction, each point of Defense Skill increases a druid's avoidance (chance to completely avoid an incoming attack) by 0.08% from the miss and dodge combined.
At level 70 every 2.37 points of Defense Rating converts into 1 point of Defense Skill.
Resilience reduces a level 70 player's chance to be crit by all attacks and spells by 0.0254% for every point of Resilience Rating, or more precisely by 1% for every 39.4 point of Resilience. Resilience also reduces the amount of damage dealt by critical hits by 2% for every 39.4 points, although that aspect of the stat exists mainly for PvP where players usually have chances to crit well above 5%, and quickly becomes irrelevant in PvE once one is immune to crits altogether.
So in order to reach immunity to crits, one needs to stack either 65 Defense Skill (or 154.05 Defense Rating), or 102.44 Resilience Rating.
The Defense route
65 Defense skill gives the following benefits to druids:
- Crit immunity via 2.6% crit reduction
- an extra 2.6% chance to Dodge
- an extra 2.6% chance to be missed
Total avoidance gain: 5.2%
The Resilience route
102.44 Resilience Rating gives a druid the following benefits:
- crit immunity via 2.6% crit reduction
While Resilience doesn't grant the avoidance obtained from Defense, the interesting side effect is that you've spent 51.61 fewer stat points to reach crit immunity, which can be spent on other stats. To complete the comparison with Defense, let's assume you add 51.61 agility. A druid gains 1% chance to dodge for every 14.7 points of agility, and 1% chance to land a critical strike for every 25 points of agility. Every point of agility also gives 2 points of armor, unnafected by the Bear Form and Thick Hide multipliers. Lastly with 3/3 Survival of the Fittest, 51.61 agility becomes 53.1583 agility.
So with 102.44 Resilience Rating and 53.1583 Agility combined, a druid gains the following benefits:
- crit immunity via 2.6% crit reduction
- an extra 3.62% chance to Dodge (1.58% less avoidance than with Defense)
- an extra 2.13% chance to crit
- an extra 106 armor
This is all basic theory, and obviously you may not be presented with such clear-cut choices in-game. It's interesting to note however that when factoring in the increased chance to be missed, the Defense route actually provides a decent amount of extra avoidance.I hope this was helpful or at least somewhat informative.
Given that the earlier bear tanking items come with Defense (Heavy Clefthoof set, Earthwarden), it's good to know that all that Defense is not quite as "inferior" as Resilience might appear to be. Earlier game content generally favors tanks with good survivability more than high threat generation. There are no DPS race-type fights where the tank's threat output determines the raid's DPS "ceiling" until Prince / Gruul. Add to that that Druids are known for their great threat generation in the first place, so a potential loss of 2.13% crit may not be as significant as a 1.58% gain in avoidance when your armor and health pool are in the lower ranges of typical druid tank stats.
As your gear improves, the importance of avoidance begins to diminish, and sources of added threat start to play a bigger role. At that point the option of gaining some extra crit chance from agility by using Resilience to reduce incoming crits becomes much more appealing.
It's important to keep in mind that both Defense and Resilience are only valuable to druids until crit immunity is reached. Once you are there, agility, armor, stam are all more beneficial on a point-per-point basis.
Lastly, Defense and Resilience stack with one another for the purpose of reducing your chance to be crit, so any combination of the two that works for you is fine.