In order of most preferable to least, this is how you would want to do things:
1) Have all the tank pieces in your bag and think on your feet, changing pieces on the fly for every encounter meaning you are 100% optimally set up for every fight.
2) Having 2 sets in your equipment manager, one for Stam/avoid and one for Armor - Letting you cover most of the options for boss fights.
3) Having only 1 set in your bag, a mishmash of Stam/Avoid/Armor as a Jack-of-All, master-of-none. Never completely bad, but never quite completly optimal either - But the best approach if you were donating for only 1 set of gear with a limited budget.
4) Having ONLY an Armor set, OR having ONLY a Stam/Avoid set. Leaving you very well optimized for some fights, and very badly optimized for other fights. Ever tried tanking HC Halion in a full Armor set? "Ouch" is the word you're looking for.
So aim for Option 1) or 2), However, if you had to go with Option 3) and make your own "Jack of all trades" Set this is how you would do:
Step 1: Choose 4 piece t10 approach or 2 piece t10 approach
If you decide to go 2 piece, you get the T10 gloves, and the T10 chest. If you go 4 piece, you have option a) 4 Piece T10 + Hit rating Helmet // OR // option b) 4 piece T10 + armor or hit rating legs.
Step 2: Decide on whether you want to go for more Armor Set focus or Stam Set focus.
Step 3: Choose whether you will wish to use Glyph of Vengeance for +10 Expertise or not, and then focus the rest of your non-tier pieces around your Hit/Expertise preferances with the following information in mind:
In my opinion, aim for a MINIMUM of 4%ish hit and 5-6ish Expertise from your gear itemization alone (Aka, without talents, glyphs or gems). Opinions will vary greatly.
Remember that you get 6 expertise from talents, 10 expertise from Seal of Vengeance. You need another 5-6 from your gear to quasi-comfortable sit at 21-22. You can gem for more afterwards if needed. If you itemize for well over the minimum expertise, then you can drop your glyph of vengeance for something else.
Expertise softcap is 26, hard cap is 56. You can (and most people WILL) passively get +16 from talents and glyph.
Hit rating cap is 8%. You get ZERO assistance from talents and glyphs.
Personally I shoot for at least 26 expertise and 7% hit rating after glyphs, talents and gems. I personally take the Glyph of vengeance and I recommend doing so because it allows for more freedom with choosing armor/hit/avoidance gear.
Here is your Shopping list: Aim to get all pieces on this gearlist
Helmets:
Broken Ram Skull Helm - Hit (Highly Recommended)
Sanctified Lightsworn Faceguard - T10 (for 4piece users who want to use armor/hit rating legs, or for 2 piece users in their frost resist set- More details on frost resist later)
Necks
Bile-Encrusted Medallion - Armor (This is strongly recommended)
Noose of Malachite - hit rating (You should try to get your hit rating needs elsewhere)
Shoulds
Boneguard Commander's Pauldrons - Avoidance
Sanctified Lightsworn Shoulderguards - T10 (1 less socket)
Capes
Royal Crimson Cloak - Hit
Sentinel's Winter Cloak - Armor
Chest
Sanctified Lightsworn Chestguard - T10 Armor. (Although I say everything is viable, I consider these chest to be one of the few pieces set in stone for an optimal BiS list.)
Blightborne Warplate - Only alternative(NOT RECOMMENDED, take the T10 ones. Only take if no one wants it for offspec or mainspec)
Bracers
Bracers of Dark Reckoning - Stam/Avoid set
Gargoyle Spit Bracers - Armor set
Gloves
Sanctified Lightsworn Handguards - T10 Armor, again one of the few pieces i consider set in stone.
Taldaram's Plated Fists - Only alternative(NOT RECOMMENDED, take the T10 ones. Only take if no one wants it for offspec or mainspec)
Belt
Belt of Broken Bones - Stam/Avoid set
Verdigris Chain Belt - Armor set
Legs
Pillars of Might - Armor
Legguards of Lost Hope - Hit Rating
Sanctified Lightsworn Legguards - T10 expertise (Taking these legs means possibly dropping your Glyph of Vengeance, at the loss of the armor/hit rating from other legs)
Feet
Grinning Skull Greatboots - Expertise
Treads of Impending Resurrection - Avoidance
Rings
Signified Ring of Binding - Armor/resistances
Devium's Eternally Cold Ring - Armor
Juggernaut Band - Stam/Avoid Set
Ashen Band of Endless Courage - Armor Proc + Hit, Kinda also a Stam set ring. (Armor proc is inferior to passive armor bonusses)
Trinkets - These are your most covetted collection pieces- AIM TO GET ALL OF THEM. You will swap your trinkets more often than you change your shirts IRL.
Sindies Flawless Fang Sindy's fang gives you awesome Stam + a Kickass defensive CD
Petrified Twilight Scale Armor. (Only activates when a MELEE strike brings you low)
Unidentifiable Organ - Armor / Stam Proc (Proc is unreliable)
These 3 are top place on the must-have list. Sindy's fang is a top tier trinket usable in almost every fight, while providing the highest stamina in the game for trinkets. PTS and Organ I consider the top tier Armor trinkets in the game, Use PTS on a slow but hard hitting encounter, and use Organ when multi tanking or tanking a fast attacking boss.
Juggernaut's Vitality - stamina (Has a different name for Horde/Alliance -Horde version linked. Alliance is known as Satrina's Impending Scarab)
Corroded Skeleton Key - Stamina
I consider these 2 about the same, JV/SIS has a better On-Use effect but the Key provides slightly better passive stamina.
Purified Onyxia Blood Talisman
Corpse Tongue Coin
Some Collection Tid Bits
Shields
Icecrown Glacial Wall - Recommended, one of the few pieces set in stone.
Neverending Winter - Only alternative
Librams - Collect them all, because why not. You can swap them mid fight.
Libram of Valiance - Str, used in most faceroll content.
Libram of Defiance - Dodge, no rampup.
Libram of the Eternal Tower - Dodge, takes time to rampup
Libram of the Sacred Shield - Block Moar Damage.
I carry these 4 in my bags at all times.
Libram of Resurgence - AoE threat.
Libram of Reciprocation - The faceroll content equiv for Valiance for when you use SoCommand
Wrathful Gladiator's Libram of Justice - Umm, cuz dispelling DP and self healing? IDK, I had it for my ret pvp set so I macro it into my flash of light spell - I don't think it's come in handy so far but maybe one day...
Weapon - I won't add any comments on these as the weapon debate for paladins is a touchy subject that needs no more input from myself
Havoc's Call, Blade of Lordaeron Kings
Mithrios, Bronzebeard's Legacy
Bloodvenom Blade
Last Word
Remember you can swap weapons in combat too. Last word's proc uptime is pretty much 100% - but the value of it is up to you to decide.
Frost Resist-An optional additional set some tanks like to carry for fights such as Sindragosa and Toravon. Also applicable for any encounter with alot of frost damage.
There is a myth that resistance caps at 415 - This is a myth that comes from misinformation based on how resistances used to work in Burning Crusade - This is no longer the case in WotLK.
That said, Resistances get more beneficial the more you have: I am not sure of exact numbers but an example is as follows:
If 200 resistance halves your damage taken, getting a mere 100 more will be equally as valuable as all of the first 200 resistance combined, as 300 total resistance will once again halve your total spell damage taken compared to having 200. This makes sense if you put it numerically:
If 200 resist gives -50%, and 300 resist gives -75%
In this fashion each additional point of resistance becomes more valuable than the last - Somewhat comparable to Armor Penetration on DPS classes, except this is a tank's equivalent for reducing Spell Damage taken.
With this in mind, please make sure that if you get a frost resistance set, you have get AS MUCH AS POSSIBLE, or NONE AT ALL - Do not go lazy half-halfs.
I believe many people who equip just 1-2 pieces of frost resist here and there without understanding the true mechanics behind resistances found that their minor amount of additional resistance did not help them very much and went around and spouted nonsense about resistance gear being "worthless" due to their own ignorance - Trust me, they are wrong, resistance gear is NOT worthless, you just need to have enough of it or you shouldn't have bothered.
Icebane Chestguard - chest
Icebane Girdle - Belt
Icebane Treads - Feet
Titanium Frostguard Ring -Ring
It is also recommended to equip your
Signified Ring of Binding if you have it.
As you must swap your Chest pieces to frost resist, 2 piece T10 users are recommended to equip their
Sanctified Lightsworn Faceguard T10 Helmet. Use
Arcanum of the Frosty Soul enchant and the
Effulgent Skyflare Diamond Meta Gem to maintain your 2 piece T10 bonus as well as maximise frost spell damage defenses. With 4 pieces of frost gear, Signified ring and the T10 helmet with frost resist enchant, it is possible to have 540 Passive Frost resist gear with the aid of a +130 resist buff such as aura.
Lesser Flask of Resistanc flasks you up another 50 resistance
With the use of consumables you can have 590 Frost resist for an entire boss fight without any professions or resistance gems.
Pattern: Fur Lining - Frost Resist - Leatherworkers can even use a spare Wrist piece they don't need for even higher resistance, putting them at a max potential of 660 >>PASSIVE<< frost resistance.
Add in a Sindy's Fang trinket and you will be nigh impossible to kill through frost damage.
I think I covered everything. In my haste to finish this post in time before Guild Raid time (30 mins ago), its possible I've forgotten a couple of pieces.
It's interesting to see people's armory's to see what results they've arrived at - Most if not all of them went through this very same process to find their own personal BiS lists that they've arrived at - Most people end up with slightly different lists.