Dark Souls, which is also one of my favorite games ever. Nothing will ever top the atmosphere of that game: the music, the ambience, the bosses... I loved how everything was connected. You can even see the Duke's Archive from where you fight the gargoyles.
Dark Souls 3 is the second favorite, since it's a epic conclusion to the series. I didn't really like the DLCs sadly, and I was expecting a lot from them.
Dark Souls 2, even with all his problem, it's still a good game, and the Scholar of the first Klin edition is even better! In this case, I prefer the DLCs over the main game (except some parts of them... I'm looking at you, Blue Smelter Demon).
I wish I had a PS4 for Bloodborne.