LEGENDARIES
Soulforge Embers - Using Flare into Tar Trap dots up to 5 targets, it's currently the best legendary for every scenario. The downside of that legendary is the positioning of the trap, which makes your gameplay inconvenient. You can use a second Flare into the same Tar Trap.
Rylakstalker's Piercing Fangs - During Bestial Wrath, the pet's critical damage is increased by 20%. This is slightly worse than Soulforge Embers for single target, but more reliable since you don’t have to play with Tar Trap. It also scales well with critical strike.
In patch 9.1 we got 4 new legendaries for each covenant:
Kyrian: Pact of the Soulstalkers - gives 10% increased critical strike buff for the whole party for 10 seconds. This legendary has high potential to be played in raid but needs specific comp in order to out-dps other legendaries.
Night Fae: Fragments of the Elder Antlers - gives double the dmg of Wild Spirits when it hits less than 5 targets. This legendary is really good for high burst which is needed for this raid tier.
Venthyr: Pouch of Razor Fragments - with every Kill Shot proc it dots up to 6 targets for 60% of Kill Shot dmg for 6 sec. It gives more sustained dmg but still depends a lot on RNG and loses value on a single target.
Necrolord: Bag of Munitions - Death Chakram applies Explosive Shot on up to 2 targets. This legendary adds more burst every 45 seconds but 2 targets is too few in order to even consider switching to Necrolord at the moment.
Raiding
Night Fae - Fragments of the Elder Antlers / Rylakstalker's Piercing Fangs- depends if you can get the full value of Antlers if not go Rylak.
Kyrian - Rylakstalker's Piercing Fangs
Venthyr - Pouch of Razor Fragments
M+
For fortified weeks no matter what covenant you are, Rylakstalker's Piercing Fangs is the best choice. However, as Night Fae Fragments of the Elder Antlers might be a good option for Theater of Pain and Mists of Tirna Scithe.
For Tyrannical weeks as Night Fae Fragments of the Elder Antlers, for other covenants Rylakstalker's Piercing Fangs.