So, after playing some more, I think Ninja is my favorite. It has everything, though it's not really the best at any of it.
It has a decent ranged attack with the kunai, but it's weak, and you can't change your attack angle, so it's worse than Archer.
It has a decent katana attack but isn't as strong or versatile as Sword.
It has a good throw, but you can't hold onto your target or change your throw trajectory, so it's not as good as Fighter or Supplex.
It has an invincible dodge that can return damage, but it requires tight timing and has limited range, so it's weaker than Mirror.
And then, on top of these, it has some unique mobility options, like a dive kick and really fast dash attack with good invincibility that takes Kirby through enemies (which is useful for switching sides against bosses), plus a new crowd control smoke bomb move that's kind of useless but hits hard.
The only thing it's lacking is an attack that goes upward, but I don't think any other class has all of these options.