Personally, I really enjoyed Dark Souls 2, despite it being made by the B team.
And right now I might have goggles on in terms of how much I enjoy Bloodborne.
But I like them all equally, for slightly different reasons. I couldn't even begin to place them in order of which I preferred.
Demon Souls hold a lot of nostalgia value for me, since I ordered mine from Hong Kong almost a year before its release in the States, which was the first time (and still only) time I've done that for any game.
They're all fantastic. I really like Dark Souls 1 and 2's story and level design, personally.
If I had to rank one as my "least" favorite, it would probably be DS1 solely because of the shoddy port to PC, but you can't really blame From for not investing too much into that, since it was a total trial run and they'd never ported a game to PC before.
Can I just like them all equally? Cause that's what I'm going to do.