Lionheart is faster, meaning less powerful Seal of Command and Crusader Strike hits, but has very slightly better stats. Stormherald wastes some itemization points on the stun proc, which doesn't work on bosses and is generally unreliable in PvE (although if you watch for it to go off, you can get in a nice Judgement of Command on trash mobs without burning a stun).
The difference among these two weapons, Gorehowl, and the Hammer of the Naaru is only a few DPS, so it's hardly worth having a big argument over. The ideal Retribution weapon is 3.8 speed (or slower, but there's only one 4.0 weapon in the game), has Strength, Agility (or crit rating), and Stamina; and optionally adds some more stats like sockets or Intellect. Remember that the itemization formula rewards items that spread their points among multiple stats instead of dumping them all in one place.
Lastly, a Human Paladin should prefer swords or maces because of the racial Expertise bonus.
And Stask, dear Stask... "necro" in this case means "necromancy", as in "bringing back from the dead". You disappoint me, young Padawan.