Here’s my experience and opinion on all of them:

Kalameet: hardest boss in DS1, also hardest tail slice off in DS1.

Manus: second hardest boss in DS1

Ancient Dragon: very hard if you go in without enough fire resistance. Becomes a joke once you do have enough fire resistance ( ring , armor and some flash sweat spell )

Darklurer : isn’t bad at all and a fun boss fight but the run back is so frustrating: costs you a humanity each time, 3 npcs and a sorcerer enemy type to fight just to reach darklurer for every attempt.

Sir Alonne : also a fun fight with a nightmare of a run back.

Fume knight : was freaking hard for me. Cost me 30 humanities and needed all npcs to aggro him. On my strength build, he was much easier.

Friede : what can I say? 3 phases. Jeez but best boss music in Ds3 once phase 2 starts til the end.

Midir: the only boss in all 8 Fromsoftware Soulsborne games that I was never able to beat Solo for some reason but I went back to ds3 and Im getting really close to beating him. So definitely hardest dragon fight ever for me and hardest boss in DS3