I have two tank specs, and most tanks who will never dps can do the same. It’s a nice situation.
When I first joined my guild, on trial, I sometimes played as a dps before securing my spot in our tank corp. At another time in the past, I had a tank spec and pvp dps spec.
This post is written for those tanks who can carry two tank specs. I’m not talking to those top 300 tanks who respec between fights, who use specialised specs for hard-modes discussed in another thread.
I’ve also used this post to provide a number of cross-links throughout pwnwear, to more detailed posts.
It should be blood. Really, there is no reason you would have anything else. Blood is frickin awesome, and ideal for single-target tanking when you do not need much AOE. It has great raid buffs ([spell]Hysteria[/spell]) and why not get used to Blood since it’ll be your tree in Cataclysm. It can be adapted to a decent AOE spec too.
I won’t go into details here but instead refer to my older posts on the various Blood specs you could choose from:
I tend to have a single-target oriented Blood spec or a balanced spec.
Here’s the interesting decision. Frost or Unholy, and which derivative? I wrote a little on the differences between trees in this analogy to lego.
Firstly you should consider raid buffs, specifically what is missing from your regular raids. This alone might lean you towards Unholy for its fantastic debuff.
Next consider utility. This could push you towards Frost for its easy snares with [spell]Chilblains[/spell]. Personally that’s what I have at the moment, in case I can get an icy touch or chains of ice onto a Valkyr in the Lich King fight.
I wrote some philosophy about utility, which is particularly relevant when you have 15% extra stamina and threat
Consider the content you are in. If you’re rarely raiding but doing lots of heroic 5-mans, and want your AOE to be kick-ass: with 2pc T10 gear and glyphed death and decay, Unholy is sooo much fun. (If you have two tank specs and you’re barely raiding, I also think you are totally awesome for dedication to tanking.)
Pick a bias. The Grid helps here. You can legitimately run a single-target oriented Blood for first spec and an AOE-oriented Frost or Unholy for second-spec. You then go into Blood for Rotface or Festergut, but the AOE spec for Valithria. That works fine.
You might prefer the versatility of a balanced Blood spec, and a second spec which satisfies your utility and raid buff needs.
In ICC Unholy is not a general-purpose tank spec, because it’s tanking cooldown does not have much uptime (due to 2s icd on bone shield combined with the dodge-nerf aura). However it’s AOE and debuff makes it fantastic for Valithria or for trash between bosses. It is a lovely spec outside ICC.
Frost’s unbreakble armour is a very good cooldown for ICC bosses, because mostly they hit physically. Its raid buff is great, and stacks personally for you. Spec advice is best sought from the post in forums and the later analysis there for 3.3.3 threat changes.