I just hit 82 on my Death Knight and am tanking normal 5-man dungeons at the moment, with intent to move on to heroics in a few weeks.
Stoneskin Gargoyle looks awfully deceptive. 4% armor and 2% stamina sounds great when you hear it, but if I think about it for 2 seconds I realize that armor isn't all that wonderful when you already have a lot of armor. I checked my stats page and that armor boost only ups my total damage reduction by an additional 1%. Stamina is nice, but I'm not hurting for it and would much rather reduce incoming damage to keep healing consistent.
SwordShattering seems a little weird with that Disarm preventing, but the 4% Parry chance appears to be fantastic. Looking at the character sheet, I can see it simply ups my total Parry chance by an additional 4%. This seems like it would reduce incoming damage far more than the 1% boost in damage reduction from the Stoneskin Gargoyle armor increase.
So generally speaking, which is better? Are there other runes I should be considering instead?