BB>DeS>DaS1=DaS2 (with DLC)
Dark 1 was disappointing to me coming off Demon's. With rare exception (Painted World), the individual area design wasn't up to par, leading to me not really giving a shit about the interconnected world, and of course the latter half of the game drops off a cliff. Dark 2 is more consistent, but rarely reaches Dark 1's highs outside of the DLC, which is excellent. Demon's still has my favorite bosses in the series, and the level design is absolutely on point and consistently great - only real issues for me are systemic, like world tendency, weapon upgrades, and encumbrance.
Bloodborne to me provides the best PVE experience with the best enemies, combat mechanics, level design that's a bit above Demon's, and my favorite aesthetics and lore - combat feedback is also on another level from the rest of the series. Sure, it doesn't have a ton of build variety, but I don't really think that's the point. I look at Bloodborne's replay value similar to Resident Evil 4's; the main thrust of replays is based on how damn good and fluid the game is, but there are some weapon and upgrade choices along the way that don't necessarily change how the game plays, but instead add different flavors to combat - think Bolt Action Rifle vs Semi Auto Rifle and Threaded Cane vs Kirkhammer: same mechanics, but an end experience that's a bit different.
Amazing series either way. I have it on good authority that Dark 3 is the series' best, and I'm looking forward to evaluating it for myself.