What is the best covenant for Death knight Shadowlands?
BIS COVENANT FOR BLOOD DEATH KNIGHT IN SHADOWLANDS
Currently Kyrian is looking like the strongest option for Blood DK in a raid setting because of the raw damage reduction it grants you. That said, the soulbinds have been nerfed pretty heavily, so it's less enticing as an all-around pick. Venthyr is still a very competitive option, and will likely be to the go-to choice now for Mythic+ or AoE boss fights. While Night Fae isn't a terrible choice, the constant nerfs have left it lagging behind most of the other picks. As for Necrolord, the buffs it received benefit Frost and Unholy far more than Blood, so it's still weak
Kyrian Necrolords Night Fae Venthyr
BIS COVENANT FOR FROST DEATH KNIGHT IN SHADOWLANDS
Frost DK is an interesting class to optimize when it comes to covenants, because the choice changes quite drastically depending on what build you're running. As a general all-purpose best covenant, I would say Venthyr is the best, since it has really good synergy with Breath of Sindragosa and works well for both Single Target and AoE damage. That said, for 2H Frost Night Fae is also a very strong contender, especially on multiple targets, and on a Single Target Kyrian currently provides the highest raw damage. If you're looking to min max you'll probably need to wait and see how the numbers shake out come heroic week, but I would say Venthyr is the safest pick at the moment.