As an addendum to what I said, the Iaito or Uchigatana are the best Katanas. If you're picking one of those you won't be disappointed, but play around with the Iaito before you kill the undead merchant for the Uchigatana. I believe the biggest difference in moveset are the R2 attacks -- Uchigatana does an overhead chop (Raises sword up, pauses, then slashes), whereas the Iaito does a quickdraw horizontal slash (Sheathes sword, pauses, then slashes). The Iaito's attack has a bit longer range, but is much easier to read (if PvP) and has more places where it'd ping off the wall.