For me it was the setting and atmosphere for Amelia that made me love the fight. With Pontiff i might have nerded out in my choice as i always loved following the background lore of that character (+ the dual glowing swords look awesome IMO).
But these things are very personal, I'm glad i managed to write some of your favorites at least :D
Been saving up some of my favorite bosses for an top 10 Bloodborne post coming soon, hehehehe.
Thanks for reading dude, game in peace!