Most runs I've seen get the Jevilstail. But isn't the Devilsknife a better option for a full game run? It does over 400 damage to King with a Red Buster, and it's more powerful than the tail. Once you get to Chapter 2, the knife speeds up so many fights. And getting the knife (and using it on e.g. King) doesn't ruin a pacifist run.

The only advantage I can see of getting the tail instead is that it can be taken off Susie and put on Kris or Ralsei instead, if that's ever necessary (it maybe slightly speeds up Giga Queen but in my casual playthrough I used Frayed Bowtie and Iron Shackle on Kris to boost his damage for Giga Queen; as far as the whole game goes I think the time saved by having the Devilsknife would be well worth it).

What do you think? Are there more reasons to get the tail instead of the knife?