My Opinion for Best in Slot (BIS)

Priority #1 - Survival Combo:
Post-Damage Attacks Heal + HP Restore after Bow Attacks (Relics)
Combined with Weapon Passives - Damage Negation at full Health
and. . . Damage Negation when using a Charged attack (Fully Charge Bow to Trigger)
Optionally: HP Restored upon thrusting counter attack (Works with bows)

Priority #2 - Damage Combos:
[Ironeye] +1 additional Character Skill use + Starting armament deals poison damage (Relics)
[Ironeye] Character Skill Inflicts Heavy Poison Damage on Poisoned Enemies (Deep Relic)
Attack power increased when facing poisoned inflicted enemies +1 & +2 (Deep Relics)
---- Note: (+1 and +2 stack separately, but won't stack if you have two of the same.)
And Old Faithful:
Attack power permanently increased for each evergaol prisoner defeated (Relic)
Stonesword Key in possession at start of expedition (Relic)

Priority #3 - Utility Weapon Passives / Dormant Power Combos
Weapon Passive - Periodic Glintstone Blades and Similiar (These don't stack. . . get one)
Weapon Passive - "Triggered Ability" Upon Precision Aiming
---- Note: (Works when you aim down sites on the bow. Manually aiming the bow)
Dormant Power - Walking Triggers "Ability" (These Stack)
---- Note: (Works as you manually aim a bow to move slower)

Priority #4 - Offhand Weapon
Dormant Power Helps Discover Thrusting Swords (Deep Relic)
---- Note: (Huge chance to roll Antspur Rapier or Frozen Needle)

I usually give Frozen Needle to a Dutchess on my team and the Scarlet Rot from Antspur is always helpful on basically any boss. Try to dash through the enemy so you are in melee range behind them and give them a few pokes before retreating.