Honestly I've not actually played that many Soulslike games, so here we go;
Demon's Souls - This has to be top spot for me based on a few things, the first is nostalgia, I remember my mate getting an American import of it since it was never announced for here in the EU, I was devastated and he came to the rescue after his holiday to 'murica, lol. I still have that playfile on my account... 1% trophy completion. One. Trophy. Yup. I then preordered the EU release and played it religiously, which brings me to my second point... it's one of my proudest platinum trophies to date. I've only got fifteen so far, but this is one of my favourites since it was such a grind to get. The third is just how engrossed I got with the game itself, spending hours and hours with duels and stuff, invading worlds, being a dick, maybe even helping people, I LOVED the gameplay loop at the time and if they ever do remake/remaster it, I'll happily try for the platinum again.
Dark Souls - Ah yeah, the follow up... this could've been first place but some of the bosses made me rage so much to the point I never actually finished the game "properly" (Cheated on PC years later, lol). Even still, the open world nature of it was brilliant, I loved finding shortcuts, wandering into areas I was clearly NOT prepared for, and working on new builds to become OP AF along the way... maybe one day I'll get the remaster for PS4 and have another bash at it, since I still remember a LOT about the game, although fuck going for a platinum on a Souls game again.
Bloodborne - Honestly I've been debating recently whether I should try and get back into this... played about 30-35 hours of the game, fought quite a few bosses (Killed the guy who fires the massive... crossbow gun thingy? at you by cheesing him off the ledge), and got that cool 2H sword that can either be a dagger or a stone/rock 2H thing which was cool... also loved the world of it, but just never really did much or finished it. It felt a little too samey in comparison to Dark Souls I suppose. I did like that the combat was faster paced though and was focused more around playing offensively rather than having a shield at all times. I also never used the gun other than for the boss on the bridge at the start.
Code Vein - Played the demo, or was it the beta, or whatever it was that released before release... can't remember. What I can remember is that I really enjoyed the art style despite some characters being WAY too anime for their own good, but meh. Gameplay was very solid and smooth, felt like I had more freedom and control over my character too... I DID finish the demo of this too, and enjoyed the boss fights while I was at it, although if I do ever buy the full game, something tells me it'll never rank higher than the actual Souls games.
The Surge - Another game I only played the demo of, never finished this demo though. Then got it free with PlayStation Plus and said I'd get into it... never did get around to that. Shame too since I really liked what I played of the demo, targeting different body parts was fun and it strangely felt a lot more fluid than the Souls games, maybe due to the higher framerate, or because character movements were looser, who knows... but I DID like it. Also it felt a lot easier than the Souls games from the getgo.
Nioh - I was in the beta for this, and not only did it kick my arse, it raped my unconscious body as it lay in a pool of its own blood, sweat and tears... tears from anger and frustration with how hard the game was for me to the point that I never even made it to the first real boss in the beta! ...then I ask why I decided to BUY it. Why? Because I did find chopping off limbs and shit to be really satisfying and I was craving a Samurai game. Shame I still have it in the wrapper, never opened. But until I do open and play it, I'll only have the memories of the beta to go off, lol.
... And that's my entire history and experience, rated from best to worst. Obviously the list could change if I decide to give Nioh a proper go, since people will probably hate me for having it below The Surge and Code Vein, but meh, it is what it is.