Anything that gives you ultimate or reduces ultimate cost. Tavas is popular.

If you are just starting out and looking to use crafted gear or gear you can buy while you start grinding for other sets then go with Hist Bark 5p and Akaviri Dragon Guard. If you have other characters you can get Dungeon or Trial gear on I would swap the Hist bark to Ebon for a start and then get Alkosh from Normal Maw as soon as you can to replace the Dragon Guard. For Monster sets I would recommend 1p Chokethorn and 1p Shadowrend for the Magicka Recovery. For endgame there is really no such thing as a "Stamina Tank" DK's go with a hybrid of high Max Stamina and high Magicka Recovery for best resource management. It helps you in keeping up block and buffing and debuffing as well as controlling the battlefield with Chains and Talons.

The Choice of your set is going to depend on the Occasion as well as on your Team and your experience. As Tank you can, and in my Opinion should, wear two 5-Piece and a two-Piece set.

Monstersets: Bloodspawn (Best set for Ulti Reg for every DK Tank), Warden, Engine Guardian, Chudan (all three in my opinion inferior to Bloodspawn)
Craftsets: Histbark (very Solid base Set with a still usefull 5-Piece on Bosses with high Hitrates), maybe Armor Master (i am not a Big fan of this set, because the 5 piece Bonus is quite worthless)
Dropsets: Ebon Aromory (Very good set which buffs your and your Groups health), Alkosh (better in a good group, since it is a set that only drops in middle weapons, schields and jewels are the Pieces you would seek), Plague Doctor (if you want to try a Tank with a high life total), Lunar Bastion ( Unfortunatly the 5-Piece is not very good, and it is roumored to have some adverse effects in Maw Vet)

For Starters you can Build yourself a Setup from Histbark, Whitestreaks and a 3 Piece Jewlery Set from Imperial City (depending on the Attribute you need the most) This is quite cheap to get. From there you can get yourself some Bloodspawn and Ebony Pieces in Spindleclutch II and Crypt of Hearts. Try to get the Undaunted Passive Going by wearing 5-1-1 and then you can Begin to grind out those Alkosh Shields and Weapons.
Also sometimes you might want to change your Setup depending on the Encounter you are facing, so carrying more than the sets you wear is Advisable.