Here is a thread from maintankadin. It's been linked elsewhere and is an interesting read.
Aside from the elitist jerks who seem to think the best way to get their point across is by insulting people (and Theckd has the patience of a saint, quite apart from anything else), the most important thing to take away from this is that picking the "best" gear for tanking is not straightforward - there isn't simply a model you can apply to decide what you should pick. The value of armour relative to HP varies depending upon:
1) the amount of unmitigated damage received in the fight as a proportion
2) how hard the boss hits (the harder the boss hits, the more valuable armour is in comparison to stam
3) the amount of heals that you receive between hits
The last one requires a little more explanation - if you are going to die in two hits, and your armour reduces the size of the hits, then your healers need to heal you for less to enable you to survive the second hit.
The thread demonstrates how just because a model can be expressed mathematically by someone who is very clever (and Theckd is indeed very very clever), it does not necessarily mean that it's the right model. It's better to take some time yourself and think carefully about why you die, and whether the mathematical model actually fits that.
This is why tank theorycrafting is so interesting. It's really hard.
From my perspective I've always loved armour as opposed to stamina. Having read this thread it's great that my instinctive preference for armour may actually mesh with reality. I've started by buying the Glyph of Indomitability to replace one of my old stamina trinkets. I have a clear premonition that Putricide will drop a trinket for me this week too...
14 hours ago