Generally, the rule of thumb to follow when trying to decide what pieces are best is that mastery/avoidance pieces provide the most combat table coverage (and thus the most survivability), followed by mastery/threat pieces (with the threat stat reforged to avoidance), followed by avoidance/avoidance pieces, followed by avoidance/threat pieces. If a piece doesn't have mastery and you're seeking the One Stat to Rule Them All, reforge the higher number to mastery -- even if it's dodge or parry.
As always, I recommend using my CTC calculator spreadsheet (I really can't pimp that enough) to properly evaluate each piece in relation to your current load-out and to confirm that an upgrade is most certainly an upgrade.
Tanking gear for 4.3
The trinkets are a bit tricky. Personally, I'm of a mind that once you're block-capped, you pile on stamina to make sure you can survive bigger hits and spell damage -- so you can imagine the soft spot Indomitable Pride has in my heart. Fine print, though: Say the tick of some environmental AoE is what brings you under 50%. Suddenly the proc is garbage for survivability in that corner case. That worries me. When a big hit knocks you to the level, that's what it will really shine -- but we need to always be aware of corner cases.
Resolve of Undying is a big, fat kiss to dodge fanatics -- 3.72% (diminished) dodge chance when fully stacked, which is a wonderful chunk of avoidance. It'll be particularly useful for any fights where the biggest damage source is melee damage.
Soulshifter Vortex makes me sad, since when we're properly block-capped, the proc is completely wasted.
Fire of the Deep looks great for a kit where you're trying to get your mastery up to the block cap level, and especially for the cooldown-esque clicky (worth 8.79% diminished dodge chance). That's an awful lot of mastery, though, for one trinket, especially when we're looking to cut back around this gear level.
For the 378 item level, the Master Pit Fighter is great for up-and-coming tanks, while the Veil of Lies' stat combination makes it a viable choice for continuing to use even into Dragon Soul.
The Light and How to Swing It shows paladin tanks how to take on the dark times brought by Cataclysm. Try out our 4 tips for upping your combat table coverage, find out how to increase threat without sacrificing survivability, and learn how to manage the latest version of Holy Shield.