Just to clarify something for you people who seems to have no clue.
Once you're at the 102.4% avoidence mark, stam is the best way to go, and its easily reachable in full 397 (dragon soul normal) gear.
For dk's however, its advicable to go 50/50 mastery / stam in your gemmng, because the higher hp pool you have, the higher your shield becomes naturally and since dk tanks are the squishiest tank regarding avoidence, its even more favorable to go for a higher hp pool.
Also for non-shield tanks its adviced to actually get some expertise/hit once you're at the level of mastery (read 28+ mastery) to make sure your threat doesn't suffer and you actually add to the dps, since in cata blizzard made this brilliant move to make sure that tank dps is counted into the dps required to down the bosses today.
Once you're at the 102.4% avoidence mark, stam is the best way to go, and its easily reachable in full 397 (dragon soul normal) gear.
For dk's however, its advicable to go 50/50 mastery / stam in your gemmng, because the higher hp pool you have, the higher your shield becomes naturally and since dk tanks are the squishiest tank regarding avoidence, its even more favorable to go for a higher hp pool.
Also for non-shield tanks its adviced to actually get some expertise/hit once you're at the level of mastery (read 28+ mastery) to make sure your threat doesn't suffer and you actually add to the dps, since in cata blizzard made this brilliant move to make sure that tank dps is counted into the dps required to down the bosses today.