Are you looking to be unkillable by standing in one spot and blocking or through self healing/mobility focus or through status effects or what do you have in mind? More than one way to stay alive through many enemies. Tank that's useful in group or for solo standing around that brings no utility to group?

Legendary Gaming on youtube has DK tank builds. https://www.youtube.com/channel/UCUD7xfRUQtEIfm_hTt80u0g
For a Stam Warden that defiles/aoe stuns/heals in negates/tanks/immobilizes/group buffs/guards etc. https://www.youtube.com/user/Shoukon32

If you're trying to be an unkillable solo tank that can tank 10+ people forever, don't bother. That got killed off with the Morrowind update.

Vigor is too expensive now (cost increase and removal of cost reduction CP) and doesnt heal for enough (since you'll probably be stacking max health over max stamina now), so you have to use Dragon Blood. Not a sustainable heal in long fights as it also costs too much to spam continuously and doesnt heal for enough to keep up with incoming damage. The Blessed CP star also took a big 10% nerf.

You'll need to get your block cost as low as possible, so you're going to have to wear full sturdy armour. Which means all the unblockable abilities in the game (backlash, destro ulti, curse etc etc) will hit you that much harder when they crit.

Run a tank if you want. Nobody here bought you the game, their opinions, as mine, as just personal perspectives full of subjectivity and bias. All worthless and meaningless unless they resonate with you.

So what if the guy wants to tank. Diversity in builds is good, even if some builds are annoying to play. If we were all dps it would be just as boring as if we were all tanks

Magplar are probably the best for tanking 5+ people. StamDK doesn't have the healing. MDK is OK, but magplar still out does it because of the far better heal IMO.

Petsorc can be a good alt tank, round trees, place mines and spam shields for a while, when around 20% streak and dark convert. No one takes out your pets because as a tank all you will be fighting is potatoes. Any quarter decent player will just ignore most tanky builds.

Tanks are only effectively used by a good group leader with the correct combo in the group. If you have 24 people and they just do whatever on whatever keep, tank is useless. You're just there to die last.

If you have a coordinated group that knows where to tell the tank to go, you're an asset. For instance,

With the DK permablock tank we run in our group we'll have her stand and attract the attention of the enemies, they all start to stack on her because of group think and mob mentality, I'm guarding and healing her on my Warden Support class and once enough are stacked they are rooted/negated/permafrosted/defiled/bombed by the rest of the group who's waiting for the moment. It's a normal thing for our group to do. If you don't have a group that will use you, they will be self-fulfilling their prophecy of tanks being useless because they don't know how to use a tank.

Tanks and supports blow solo or with bad leaders of groups who don't utilize them. They also multiply the effectiveness of a group with a good leader and group. If the bomber and negate just went out there with no tank, the enemies would not be stacked and there would ahve been no roots or permafrost to keep them stacked and defiled.Just how that is.

I've also tanked with DK as Permablock, Magplar and Warden. If you want to stand and block and guard go DK for they are the best at this becausse of passives.

If you want to be able to bring utility to the group and group defile at will/throw quick heal ulti which you can place at range AND spam heal
that gives all allies healed 10% more max hp while your ultimate is healing w/ Major Mending procing & permafrost slow & stun, aoe root, aoe minor maim, aoe major resistances for your group, heal in negates while guarding go Stam Warden.

If you want to be pretty tanky, but rely on healing more than resistances then go Magika Stamplar. Negates just kill you because you have low stamina to roll out of negate and can't mistform out. I use to run this and Warden is hands down better. One thing Magplar has over Stam Warden is that Magplar have a cleanse and if you can't aim Breath of Life is good, but only heals 2. The heal ultimate is great from magplar because it autohits who you need to hit, but it has a limited range and is expensive and you're casting and can't do anything while casting your ultimate for those few seconds. Also, no major mending