I'll never understand why people tend to speak in absolutes. It depends. It always depends.
It depends on your gear, your playing style, your team, and, of course, it depends particularly on the opponents you're about to fight. Plus maybe other factors i forgot.
So,
- if your healers complain: "you take too much spike damage!" - take armor
- if they complain: "you suck too much mana!" - take dodge
- if your DDlers complain:"we need to hold back!" - take agility
- if you're a progressive raider, and are about to fight new bosses soon which you don't know how hard they hit - take armor
- or you already know how hard they hit, but you feel your Effective Health is sufficient - take dodge
- if you're rather a casual gamer and think you'lll get geared right soon enough for new fights either way - take the one that makes you feel best, or that best fits your character
... and so on
PS: My first post on this great forum, though i'm reading it for a while. Hello all, it's good to be here.

Hope my english is understandable.