[bVR14 ]Twin Sister Set[/b]
(2) Adds 120 Stamina Recovery
(3) Adds 900 Maximum Stamina
(4) Adds 640 Weapon Critical
(5) When blocking, 20% chance to cause attacker to bleed for 8000 Physical Damage over 8 seconds. Attacker must be within 5m.

Last time, permablocking build with a medium armor is not as good as using heavy armor. That is because last time you can only reduce the cost of blocking through the following factors:
1. Heavy Armor passive "Bracing"
2. Jewelry Glyphs (Shield-play enchantment)
3. 1 hand & shield weapon passive "Fortress"

This time in 1.6, with the addition of champion passives:
1. Heavy Armor passive "Bracing"
2. Jewelry Glyphs (Shield-play enchantment)
3. 1 hand & shield weapon passive "Fortress"
4. Champion Passive "Block Expertise"

So now it is possible to block with a medium armor. And when we say blocking with medium armor, nothing works better than the Twin Sister Set because of its
5pc bonus set.

This Permablocking Twin Sister Build is a build balancing the tankiness with awesome amount of DPS, and it can have many variations depending on your playstyles.

DPS Oriented variation
Combine Twin Sister Set with Shadow Walker Set
(2) Adds 166 Weapon Damage
(3) Adds 877 Maximum Stamina
(4) Adds 117 Stamina Recovery
(5) Restore 975 Health and Stamina every second while hidden and not moving

To reduce the cost of blocking you need to enchant all the 3 Shadow Walker jewelry with Shield-play enchant.
The Maximum Stamina and Stamina recovery provided by the Twin Sister and Shadow walker set can negate the stamina that you will loss due to blocking.
Use 4pcs of armor and 1 Axe for Twin Sister.
The reason why we need to use Axe instead of full 5pcs armor is that we want to have 1 more slot for armor along with the shield. Those 2 pcs should be craftable set with Nirnhoned trait to be able to block more effectively against spell damage attacks.

Medium armor passives "Wind Walker" and "Agility" will increase your Stamina Recovery as well to negate the loss of stamina thru blocking, and increases your weapon damage.

Night's Silence Set
(2) Adds Maximum Stamina

You need to be a Werewolf to get additional Stamina recovery

So the concept here is getting lots of Stamina and Stamina Recovery for increasing your damage and sustain and negating the cost of blocking.
The 5pc bonus of Twin Sister Set will proc a lot, damaging enemies while you block. With this build you can permablock certain number of enemies.
I would say 4 to 5 average players at once.
This build works best for Nightblades because of their ability to hide. The 5pc bonus set of the Shadow Walker build will keep them alive if they're in trouble.
Using Shadow cloak skill will bring their health and stamina almost back to full while using magicka. That is a concept of self-sustaining when you use 1 stat
to regenerate 1 or 2 other stats.

But this build will also work fine for Dragonknights because of their ability to self-heal instantly using Green Dragon Blood, and that skill will increase their
stamina recovery as well. For DK tho, they dont actually need to get the 5pc bonus of the Shadow Walker. They can go for 3pcs of the craftable set that gives stamina, stamina recovery, or weapon damage. It depends on what you will choose for your playstyle, that's why this build got many variations.

Obviously the weapon to use is 1hand & shield. For the secondary weapon, use Two-handed weapon.
Two handed will be use for the healing that rally gives (specially if your NB), and the amount of damage you can deal to enemies, you know what I'm talking about
2-handed weapon here.

For 1-hand weapn skill bar
Since we can do block casting, it is good if you will utilize few skills from 1hand and shield weapon.
1. Invasion - this is a must to close the gap since the Twin Sister bonus only affect enemies 5 meters away from you. You can not let a long range caster spam his spells on you, you want him to receive that bleeding damage from you Twin Sister. If you're close to enemies and they hit you all they want, they wont notice their hp drop so quickly and you only have to do few attacks and they will be dead.
2. Heroic Slash - this will give a decent amount of damage because you will have high amount of stamina. It will also snare them 60% for 12 seconds. It will also afflict them with Minor Maim debuff reducing their damage by 15% for 12 seconds. And it will grant Minor Heroism for faster ultimate regeration.
3. Defensive Instance (optional)- this will make your block mitigation increase by 8% and further reduce the cost of blocking by 8%.
4. You can use any class skill that will be best fit for your style
5. Same as 5
6. Choose what you want

For 2-handed weapon
1. Rally - For healing and increasing your weapon power
2. Critical Charge - always a good way to have a gap closer that can deal good damage
3. Wrecking Blow - widely used skill now. Great damage!
4. Executioner - in Mortal Kombat this is called "Fatality"
5. Your choice
6. Your choice

This is 1 variation you can go with Twin Sister Set. The other variations I'm talking about is changing the Shadow Walker Set with another set.
The main concept tho, is to permablock and let enemies damage themselves. Then go for the kill once you notice their hp drops.
With this build you got survivability thru tankiness and sustain, and damage from your high weapon damage and bleed from Twin Sister.
They thought the set was useless, the gears were sold as cheap as it can be. But this set still sells for 248 AP on Cyrodiil, because this set is awesome!

This post to be updated for other variations.