Alright, I'm still playing through the games. I've gone through Demon's; Dark Souls 1 & 2, and am about finished with Bloodborne now. I am on the final guy in the main game, but finishing up the final boss of the DLC, which for me is Orphan of Kos, as I already went back and fought Laurence, The First Vicar. So far, Kos is posing a challenge. I got his health down half way, but he got the best of me, so that means I have to go upgrade a bit more. I also have to go through the Upper Cathedral Wards, which I hear has one of the toughest bosses in the game. As for the DLC, it was actually not that hard other than Ludwig depending on level. I don't think the recommended level, which I believe is 63 or something, is a high enough level at all. I couldn't get half his health down at level 67, and though I beat him on the first go when I went back later, he still posed a good challenge even as I was at level 105. I think I can beat Orphan pretty soon here. Anyways, sorry. That was about bosses for sure, but I was more talking about where I am at now.
As for hardest and easiest bosses in the series so far, which I am putting Bloodborne in this, though there are no bosses in it that I'd say are the hardest yet, are for me, Ceaseless Discharge from the first Dark Souls, and Old Hero from Demon's Souls. They posed the most challenge for me personally, and had me go do many other things before I could get to them again. I also feel like I beat them just before they were about to kill me. They were the ones that no matter what level I was at, as I kept coming back, they were still challenging. From what I understand, Old Hero can become really easy if you pick up a specific ring, and Ceaseless Discharge can be exploited with the stairs, though I never picked that ring up, and that exploit didn't work for me. As for easiest, I think the easiest were probably Pinwheel from the first Dark Souls; Old Monk from Demon's Souls, which I feel may be unfair, since it's supposed to be a PvP battle, but I fought an A.I. and Witch of Hemwick in Bloodborne.
When it comes to my favorite, I'm not really sure. Many of them are great. I liked in Bloodborne, Micolash. He wasn't the funnest to fight, so that disqualifies him in that regard, but I felt he was pretty unique in how you had to chase him, and he had some personality as you went through it. So, what about you? I don't mind if you mention bosses from Dark Souls 3. In fact, I'm interested to know about how hard or how easy they are. Off topic, but you know what I just discovered?... I thought I had only the Upper Cathedral Wards to go, but looks like I have Forsaken Cainhurst Castle as well... Jeez. This means another area, and another boss, which is Martyr Logarius I see. Furthermore, sorry for those that are tired of Souls threads, it's just that I'm still in the middle of getting through them, so they're the games on my mind most right now, and I'd like to discuss it with a new thread, or threads.
I noticed I didn't mention anyone from Dark Souls 2, though there's some worth mentioning. The Ruin Sentinel's gave me some trouble, and were really intense. To me, they were the perfect example of bosses that need good timing to hit. Perhaps it was because I went there right near the end of the game, but I'd also consider Dragonrider as one of the easiest bosses in the series, as well as Prowling Magus and Congregation. I actually hadn't beaten the end bosses of the DLC areas. They'd take quite a bit of grinding, and I wanted to move on to Bloodborne.