It's been said plenty already, but the debates will always rage on (which is healthy sometimes). There is alot more to tanking and staying alive than simply "avoid as much damage as possible" and its generally people with that mindset that end up being those spiky hard to heal tanks. Right now, being able to predict the damage taken, and control that damage taken, far outweighs avoiding as much as possible. In this light, for warriors and paladins anyway, mastery is by far simply the stat to go for.
Dodge and parry are important, sure, they always have been, but its never been wise to stack it, and still isn't. Why? Because its not predictable. Yes it'll occasionally be that thing that saves you from dieing when you avoid that hit at low health, but just as much if not more, its the thing that fails and you end up dieing anyway.
Stamina..its not as important as it was in Wrath, no, but its still important. But not important enough to gem for outside of say...20mastery/30 stam gems, and the helm/shoulder/chest enchant. All of those things will most likely provide you with all the stam you need, given you are wearing 346/359/372 gear.
Someone said above the exact pattern I'm following right now as far as gemming as a prot warrior.