There are a lot of topics on the net regarding the hardest bosses of Bloodborne, but not very many relating to those bosses that are just BEAUTIFUL...in a sense.

Henceforth, let's discuss a bit about which bosses you've really enjoyed fighting in Bloodborne, either because of the mechanics involved, or because of how visually / thematically interesting the boss was in itself.

Best boss: Father G
Hardest boss: Ebrietas. The only one that gave me a hard time trying to beat it.

The first hunter boss and the last one

I haven't gotten the true ending, since im doing a blind playthrough without any help from the internet or anything and ive already gotten the other two endings, so i dont know of any of the last bosses in the true ending "route", i know there is a door in the boss area where you fight "Micholas, Host of the Nightmare" but i havent found out the key to open that door...

 So far ive finally gotten all the NPCs in the Cathedral Ward (the Asshole gave some troubles since i had to figure out his gimmick by myself...)

 im also doing the Eileen quests, already did the second part in the grand cathedral which i didnt find in my previous playthrougs and im currently trying to find out where she will be next

 im hoping any of those will end up giving me the key to that door on the boss area that i mentioned before, and im hoping to find the third umbilical cord in the area behind that door, since i already figured out by notes in the game that i need three umbilical cords to get the true ending, (at least that's what i assume) anyway im not asking for help or anything just mentioning why i don't know of some possible bosses including the true final boss.

 so to answer your question my favorite Bosses so far are

 1) Father Gascoigne

 Boss fights were you fight a character that is essentially the same to you are the BEST ones, (just like Dante vs Vergil or Jehuty vs Anubis), the flow of the fight the agressivenes of father Gascoigne the setting with all the toombstones the incredible music... its just Amazing!.

 Add to that the fact that there is a story behind Gascoigne, how he killed his wife (who can be found in the boss arena) when he fell for his "beast instincts" and the daughter he left behind... truly sad... but unlike most fights in the soul series the Story is not just and add-on or an explanation to the fight, but it can actually have some use in the fight, if you decide to use the music box and make him remember the life his leaving behind which makes him stagger and transform more faster.

 which leaves me to the second reason why i love this fight and its that it fits the LORE PERFECTLY, in a world where people are losing they're minds and transforming into beasts you get to fight a hunter, who is going through the whole process while fighting you and ends up transforming at the end into the same beasts he was fighting, its one of my favorite boss-fights in the soul series by FAR.

 2) Gehrman the First Hunter

 Mostly the same reasons why i like Gascoigne:

 - a Character thats just like you with youre same abilities (for the most part)

- incredible music

- amazing arena for a final boss-fight

 but there are some reasons why this fight is special:

 - unlike all of the previous bosses Gherman isn't fighting you because he wants to kill you (well technically he does XD) but hes doing it to free you from the nightmare and end you're "hunter life" so you can move on with you're real life.

 - Gherman actually really wants to DIE, if you approach him trhough out the game you can hear him speak while sleeping in his chair, and "he calls out to Master Willem and Laurence asking for them and telling them that he is incredibly tired of his incredibly long life and that he just wants to be out of the nightmare", but of course he cant since he is kind of the "HOST" of the Hunters Dream, so by you actually killing him in that ending you are doing him an incredible FAVOR.

- The Cleric Beast

 there is nothing really especial about this one, but i just really like the boss design and the AMAZING music (probably my favorite track in the game)

- Master Logarious

Just like the previous ones im sure there is some deep lore to this one as well, but i haven't found it all yet, so far im sure he went in a crusade to stop the vilebloods but something happened and im sure that what our "cleric friend" (whos name i cant recall) tells us is in part fake, since i believe that Logarious actually decided to stay in Castle Cainhurst and guard the invisible door that leads to the leader of the vilebloods, whos actually a lady... which makes me think that maybe (just maybe) there was a relationship between the two...? (there is afterall a second throne next to her so she must have someone “close to her”) anyway im still investigating by my own so this is all just my speculation and im sure his lore must be already explained on Youtube or any "Souls site"

Aside from that i really like how he can switch styles between magician and a really good melee, his soundtrack piece... i don't even remember it sadly...

Anyway if you people know stuff related to bosses that i dont know off, or lore or anything that i dont know please DON'T tell me, i want to figure it out all by myself

I hated Logarius with a passion. He was the first boss that actually made me go "Fuck this, let's ring that fucking bell and get some help for this bastard". But yeah, his lore seems really cool...and considering what an ass Alfred himself is, I can't help but side with the vilebloods as well.

YEAH!, he is really tough but i like that a lot, since i love challenges and he provided one of the best ones!

and you are also right about Alfred, what he did to that woman is TRUE evil, but more importantly the things he says after that something along the lines of: "now the master can be cannonized as a true Martyr" which makes me think that he KNOWS that Logarious WILLINGLY left the church to join the vilebloods and he is trying to hide that truth.

and the reason why he HATES the leader of the Vilebloods so much is because she must be the reason why logarious left the church, possibly because he fell in love with her, (but again that is just my speculation).