The Warden Tank is a very nice option for Tanking in The Elder Scrolls Online. They have been built well for Tanking and they are well equipped for the job along with helping group members ability to survive. They improve survival by providing allies with Major Resolve via Frost Cloak which adds 5280 Resistances to anyone in range which is a huge 8.8% Damage Mitigation. Warden Tanks also have the Maturation passive which provides the Minor Toughness buff increasing allies Max Health by 10%, to maintain this as a Tank you need to use an AoE Heal such as Orb. Wardens also provide a range of other group buffs including added recovery with Enchanted Growth and also enemy debuffs including Minor Vulnerability with Fetcher Infection, Off Balance with Cliff Racer and AoE Major Breach with Deep Fissure. Other group support offered by the Warden Tank includes a heal to 1 ally with Polar Wind and a group synergy with Budding Seeds. When it comes to dealing with multiple enemies and crowd control, the Warden Tank is almost as well equipped as the DK Tank. The Warden Tank has Gripping Shards which is a really nice Tank ability as it is a 360 degree immobilise and snare which roots enemies in place. The damage caused by Gripping Shards and chance to apply the Chilled status effect are both scaled with Max Health which for a Warden Tank is obviously very nice. For pulling in enemies you can use Frozen Device which teleports the enemies to your location, and costs Magicka which is great. Frozen Device is best used in situations where you know where an enemy will spawn, and you can pre-place your Portals so that the enemy will teleport to you as soon as they walk into the Frozen Device. It can often be difficult to place this accurately, or on a focussed target mid-combat which is where it is sometimes better to use Sliver Leash from the Fighters Guild Skills are this Chain works a little quicker than Frozen Device. Other good things you might find with a Warden Tank include Shimmering Shield which is a huge Shield which can completely absorb some projectiles that you would usually need to block or they would kill you in 1 hit. Sustain is quite good for the Warden Tank and you also get a free Purge by using the Betty Netch. Self healing on a Warden Tank is extremely easy with Polar Wind which is a Burst Heal and a Heal over Time plus it will heals 1 nearby ally, all of this scales with Max Health meaning the healing from it can be huge especially when it crits.
A lot of groups usually opt for a Warden Healer, in this situation a lot of your group benefits become a little redundant. If you are using a Warden Tank in a group with a Warden Healer it would be a good idea to discuss who will use what abilities for the Buffs and Debuffs, if a Healer uses Frost Cloak then you can use Balance for example.
Overall the Warden Tank is an incredible option for Tanking, especially if you are a newer Tank and looking to assist in your own and your groups survival. Wardens Tanks are an all round good option for all content.