What is general opinion on the best dropped sets for tanks? Overland or dungeons. Either is good.
The basic sets for any new tank are Hist Bark (heavy, sturdy), which is craftable, and Werewolf Hide, which drops in Glenumbra. The WW set gives you ultimate generation on the 5-piece perk. A nice drop set to replace your Hist Bark when you can, is Ebon Armory, which drops in the Crypt of Hearts dungeon (both I and II versions). It improves the healing you get and gives your team a health buff. Again, most people prefer sturdy trait on their Ebon, because it makes it easier to block.
Many (most) tanks also run the Bloodspawn 2-piece monster set for even more ultimate generation, the helm for which drops (guaranteed) from the final boss of vet Spindleclutch 2 (which is sort of a medium-difficulty vet dungeon. Once you're up and running as a tank, if you get lucky with two good DPS and a healer in the group finder, you should be able to complete.)
Alternative drop sets include Roar of Alkosh, which drops from the Maw of Lorkahj trial and debuffs your enemies, and Plague Doctor, which drops in Deshaan and buffs your health.
You can check out Youtube videos by Alcast who has info on some of the most popular tank builds.
When you put your gear together, don't forget Shield Play glyphs on your jewelry and defending/decisive traits on your weapons.
I run a Health Tank, so I use Plague Doctor. Hist Bark is my craftable set, and I have not found a better alternative to use. Sure, everyone says Ebon, but I don't see the trade off in Attributes and Stats on my tank being better than giving DPS's another 1000 Health. They just need to stay out of the Red.
My Monster Set is Bloodspawn for the Ultimate Gen. The Chudan set that drops in Mazzutan does have some awesome Tank Stats so you can chase other stats rather than resistance on the other gear sets.
Ebon is good for really difficult content, like trials and Hist/Horns DLC vet dungeons, where the 1k health can often make the difference between an alive DD and a dead DD.
Otherwise, it's not really necessary, and combinations like Nestor mentioned, or Torug's to make Crusher stronger, are nice options.
My suggestion would be, create two or three combos and take them into the dungeon with you, and swap them out as required. I use the addon "Dressing Room" that lets me swap between Plague Doctor+Ebon and Plague Doctor+Torugs with a simple keypress.
Didn't see anyone mentioning Akaviri Dragonguard but might have missed it (magicka regen, healing taken, health, ultimate cost reduction 15%). Very good set as well, drops in Eastmarch.
Torug's/Alkosh+Ebon/Plague/Alkosh. (Obviously if your choice between the first 2 is Alkosh you chose Ebon or Plague as your 2nd set.) That plus your choice of Monster set, Bloodspawn, Lord Warden, Shadowrend+Chokethorn combo or other, personal favorite is S+C combo, great for magicka sustain.
Anyway, those combos for 5p sets will give you great stuff for both Veteran Dungeons as well as End game Trials, they are common sets used by almost all end game Tanks. There are other set ups too, such as with Dragon Guard for the ulti cost and regen, but its not as common, but can be great in some situations. I personally do dungeons with a sorc tank that uses Dragon, really great for utli tank set up.