I tried Hammer of the Righteous with 2 weapons below and there was no big difference between Hammer of the Righteous damage of those weapons:
Weapon 1: 528 Hammer of the Righteous damage per target
King's Defender
Binds when picked up
UniqueOne-Hand Sword
98 - 182 Damage Speed 1.60
(87.5 damage per second)
182 Armor
+28 Stamina
Durability 105 / 105
Requires Level 70
Equip: Increases defense rating by 13 (5.5 @ L70).
Equip: Improves hit rating by 17 (1.08% @ L70).
Weapon 2: 582 Hammer of the Righteous damage per target
Merciless Gladiator's Pummeler
Binds when picked upOne-Hand Mace
177 - 330 Damage Speed 2.60
(97.5 damage per second)
+27 Stamina
Durability 105 / 105
Requires Level 70
Equip: Improves hit rating by 10 (0.63% @ L70).
Equip: Improves critical strike rating by 19 (0.86% @ L70).
Equip: Improves your resilience rating by 12 (0.3% @ L70).
Equip: Increases attack power by 30.
HotR deals 120% of you weapon damage and it is done as Holy Damage and so doesn't get reduced by armor unlike your normal weapon swings which do suffer from it