Yes yes I know there's a lot of posts. I thought I might create one here so people can refer to this one.
Go ahead and debate.
I personally thing Cold Iron Vanquisher is equally as good as Leviathan, knowing that both swords with triumph at the same attack strength at lv 10.
And with cold iron's undead perk, a smaller amount of weakness is worth dealing with.
"knowing that both swords with triumph at the same attack strength at lv 10."
The stat bars are wrong. The Vanquisher deals significantly less damage to all enemies, and only deals -slightly- more damage on Undead than the Leviathan. On top of this, the Vanquisher's charged attack has much less knockback, leaving you wide open to counterattack.