F.Y.I: All the stats on these pieces of gear are changing in 3.0. I will need to revisit this post soon.
I see the "What Should I Buy First" question come up all the time on Maintankdin. Then I saw this excellent blog from Tanking Tips listing the Badge Purchase Order for Warrior tanks. It's a great read, but as a Tankadin I look at gear a bit differently than my Warrior brethren.
So here is the Honors Hammer Badge Purchase Order. Questions, Comments and Concerns are always welcomed.
Don't follow this list blindly. If you are really weak in one particular area buy that first. For instance if you have been running Kara and have most all the epics there but Nightbane just won't drop the Panzar'thar Breastplate, the Chestguard of the Stoic Guardian moves way up the list for you.
The Top 10
#1 Libram of Repentance - At just 15 Badges, its a quick and relatively painless piece to get. Uncrushable is a major milestone goal for every Tankadin. It's simply a tougher goal to achieve as a Paladin than as a Warrior. As you gear up getting Uncrushable becomes easier, and this Libram will help you swap out gear, staying uncrushable and increasing your stamina, and avoidance.
#2 Inscribed Legplates of the Aldor - These are new in 2.4, and they rival a drop from Black Temple (Praetorians). That puts them way up on my shopping list. When I looked at these on the PTR, I was amazed at how well Blizzard had itemized them for Paladins. 100 Badges is a steep price, but these pants are hot and worth every last one. Also worth mentioning here are the 2.3 Badge Legs, the Unwavering Legguards. Unwavering Legguards are itemized for AoE tanking and you should consider them if you don't have Tier 5. However, the Inscribed Legplates will do a decent job as AoE pants until you get T5 or Unwavering, and still be superior to either on bosses.
#3 Ring of the Stalwart Protector - Armor, Stamina, Dodge. That's an incredible triumvirate of stats on one item making this is an excellent tanking ring. Unless you have both the Ring of Sundered Souls from Morogrim and the Band of the Eternal Defender, it's probably better than one of your rings right now. Eternal Defender requires Exalted Reputation ring from Scale of Sands in Mount Hyjal. Not only do you have to be Exalted but you have to have killed Kael and Vashj. No, you don't need them for attunement, but the ring is a reward from turning in the Vials quest.
#4 Slikk's Cloak of Placation - Just like with the Inscribed Legplates, Slikk's ranks right up with some of the best tanking cloaks available like Pepe's and Pheonix Wing. All 3 cloaks have their uses and ultimately, you'll want all 3. It's a relatively inexpensive purchase, and provides good bang for your Badge buck.
#5 Chestguard of the Stoic Guardian - Next up, is the 2.3 Paladin chest. It is well itemized and is roughly equivalent to the Tier 5 Chest that drops from Kael'thalas. 2.4 introduced a new Chest, the Shattrath Protectorate Chestplate. I still find the 2.3 chest superior. Stoic Guardian has Dodge instead of Spell Hit, and you can gem the Stoic Guardian to have just as much or even more stamina than Protectorate since it has 2 additional gems slots. The 2.4 Chest works well in a Threat set, but 100 badges is a ton to spend for such a situational piece.
#6 Sabatons of the Righteous Defender - These are roughly equivalent to a Tier 5 boss drop. I won't replace them until I get the Tide Stomper's Greaves off of High Warlord Naj'entus in Black Temple. Even after that, the boots will have a home in my Block Value or AoE set. The new 2.4 boots, Blue's Greaves of Righteous Guardian are worth mentioning here. With their high block rating, they are fantastic boots for Uncrushability. You may be struggling to reach Uncrushable now, but as you progress you won't be. You'll want to trade some of your excess Block Rating for other stats like Dodge and Block Value. 75 or 100 badges is no small investment. You want that investment to last a long time, and you will simply get more wear out of Righteous Defender than you will Righteous Guardian.
#7 Libram of Divine Purpose - Believe it or not, there are times when you don't need to worry about being Uncrushable. This includes nearly all trash, Heroics, and 5 mans. (The Trash mobs in Magtheridon's Lair can crush). During those times, the extra threat from this Libram will go a long way.
You still want Repentance for AoE tanking as the extra block rating helps once you blow through your 8 Holy Shield charges. This is also a great Libram to have while you are soloing.
#8 Empyrean Sapphire, Seaspray Emerald, Shadowsong Amethyst, Crimson Spinel - These won't be available until you realm has completed the Alchemy Lab addon on in Phase 4. Much like the Anvil was an add on after you took back the Armory, the Alchemy Lab is an add on you build after you take back the Harbor. Each Gem will cost 10 Badges of Justice. At the same time Shaani starts selling the gems, she also will be selling the patterns to cut them. The main one you are after is Empyrean Sapphire which will cut into Solid Empyrean Sapphire, the big brother of the Solid Star of Elune. The uncut gem are also available as drops from Magtheridon, and can be cut by any Jewelcrafter with the appropriate amount of Reputation with Scale of Sands (Mt. Hyjal).
#9 Battlemaster's Audacity - Spell Damage with an on use health increase. This is like a mini Last Stand. It's a very nice trinket. It's only low on the list because you have an alternative way of getting it. It can be purchased with Honor Points from Battlegrounds. I know from personal experience that PVP as Prot is rough. But Battlegrounds are an order of magnitude easier on you than Arenas. Run Flags, and Guard Points. You are a Protection Spec Paladin. You take not dying to an artform! Icon of the Silver Crescent is another good Threat piece. It has an 'On Use' ability that will really kick your burst threat into high gear.
#10 Expertise and Hit pieces
Expertise is not quite as powerful for Paladins as it is for Warriors, but we shouldn't over look it's benefits. If we miss the mob or Boss, our Seal won't proc and we'll lose a bit of threat. It has been demonstrated that 1 expertise is rougly equal to 1 spell damage once you hit around 825 TPS.
Expertise also helps us avoid the infamous 'parry gib' where the Boss parries your attack, and then attacks faster, causing you to take a sudden burst of damage that your healers might not be able to react to fast enough
The place where Hit Rating really helps you out is with Taunt. Our Taunt is based on the melee hit table, which means that Hit Rating will reduce the chance of a taunt resist.
There are some fights (like Bear Avatar in ZA) where a taunt resist can be a killer (litterally).
Your Expertise and Hit items include: Girdle of the Fearless, Bracer's of the Ancient Phalanx, Brooch of Deftness and the Bonefist Guantlets. These are a purely situational pieces but very powerful for those situations.
Also I recommend not buying a Badge Belt until you have gotten a Belt of the Guardian made. Either spend the 30 Badges for the two Nether Vortexes or buy the Vortexes off the Auction House or your local Tier 5 guild.