Here's an alternative perspective because, even though I know I'll be downvoted for it, your least favorite is my most favorite.
From best to worst doesn’t really work here, so I’ll list from best to least best:
Dark Souls 2: SOTFS. DS2 was probably the worst game in the series on release, but IMO they fixed the issues that mattered most and made the biggest and best title From Software has delivered. Every complaint people level at it is about window dressing details for me, while the core experience rises above all else. I get that as a matter of taste it will always be the least popular due to the heavier and more deliberate feel, but since I like that, my attention is drawn to everything that should be praised. Unique areas, interesting weapons, plenty of great bosses, cool features like NG+ changes, tons of DLC that could have been a game in its own right, unique and interesting stories and characters, cool mechanics like the dual wielding and bonfire ascetics.
Dark Souls 3. If you loved DS1, which I do, I don’t know how you could rank DS1 above DS3. DS3 is the new and improved DS1. Insanely polished and fluid, and directly revisiting and building on the lore, I understand why people rank it above DS2 even if I don’t. From’s experience really shows here. If it weren’t for DS2’s sheer size, my love of the complexities some people hate, and DS2 being the most balanced in the series PVP-wise, this would be #1 for me.
Demon’s Souls. This game was like a miracle, but it’s knocked down in the list by it’s age and sleeper budget. From really did a fantastic job with it, but a lot of what made it wonderful was its newness and the community it spawned. Some of what made it great seems to have been purely accidental – the PVP was amazing in part because of unplanned glitches like spell cancelling that actually accidentally balanced the game. For what it was in its time Demon’s deserves the top spot, but I’ve gotta be honest, DS2 and DS3 are just better.
Bloodborne. IMO, this is the best single player game from has made. It removed shields and gave you a ranged parry instead, which was a nice change up. The lore and atmosphere was as fantastic and dark as Demon’s Souls, a different flavor than the Dark Souls games, but with all the polish of DS3. The procedurally generated challenge dungeons extended that sense of discovery and exploration that ends with NG in the other games. The only game with more non-multiplayer variety and replay-ability is DS2:SOTFS. The multiplayer was a throwback to Demon’s Souls, a little more awkward and random than the Souls games, and with silly OP weapons the PVP was too often down to 2-hit fights – but the speed of play was a lot of fun.
Dark Souls 1. The nostalgia is real. I put more hours into this than any of the other games. I think the story lore and world are even better than Demon’s. But if I look at it objectively, it had the rushed areas (so did DS2, but they fixed DS2 and never really fixed DS1 even in the remaster), it was the least balanced, and some of the mechanics didn’t hold up well. As it aged a lot of Demon’s players felt more and more disappointed because the depth added by Demon’s Souls “glitch” mechanics was removed, polished out, showing some of the special things about that game to be unintended. The remaster made it even worse, patching out dead angles for example. I loved it, but in comparison to the other Souls games it’s simply dumbed down.
Sekiro. It’s like a Souls style boss-rush rhythm game. It’s beautiful, I love it, but it’s longevity is based on that rhythm game style challenge. It’s an interesting element of the Souls-style gameplay to focus on, and a great entry in From’s library, but I don’t think it stands up to the other games as a package.
DS2: Vanilla. Release was horrible. You could play for a month and only run into another player if you were lucky. A lot of animations were broken. Soul Memory was just awkward until the Agape Ring was added to the game. The bones of greatness were there, and a lot of wonderfully fresh ideas, but it just wasn’t ready for prime time. But I’ll always be grateful for whatever disasters birthed this monster, because my favorite game (SOTFS) only exists because From did what they had to do to polish this turd, and the chaos of its development probably put a lot of cool mechanics in that might not have been there if it had been rebuilt prior to release. Maybe it’s not a popular opinion, but IMO they redeemed it completely and the ugly artifacts that remain in SOTFS are just minor distractions.
King’s Field. Just kidding. I never played these games I have no idea.