What are the hardest chalice bosses?

I always like to fight the toughest enemies a game has to offer and I already defeated main game and DLC bosses.

So far the ones I've met in dungeons are shit there was a pig, a brainsucker, three fat guys, some flaming dog and that fireball throwing minotaur thing as well as Celestial Emissary who didn't even have his minions making the entire fight a joke. Is it worth it to buy Lost or Uncanny versions of weapons by the way? What are the differences between Lost and Uncanny?