This include Demons Souls and BloodBorne, as well as Nioh, despite it not being a BloodSouls game.
My favourite Souls Boss is probably either Raime for being a thrilling fight against a badass knight or Artorias for being a fast paced battle that puts your experience as a player to the test.
My least favourite is the Bed of... Actually, I like that fight. It's Elana for her bullshit summoning mechanic. Especially with my luck, which basically means that 25% chance she'll bring out Velstadt equals most of the time. I used to despise the Pursuer, but I got good.