I love all of those games. It's not a competition, of course; they each occupy enough of a space of their own that they can all exist side-by-side.
While Nioh's combat is ostensibly deeper, and Souls/Bloodborne offer more 'options', Sekiro feels like it is in another league to me.
Sekiro's combat is fast, fluid, tactical and, most of all, tactile in a very 'real' way that the other's don't quite match. What it does, it does so fucking right. It is lean in comparison to the others, sure, but I find it never less than compelling.
The inversion of defence and offence means you're always on the attack, which gives a (hyper-)real sense of sword combat. That back and forth of battle is always tense and the deathblows that punctuate battle are thoroughly satisfying moments (as well as a moment to consider your next move or, later on, launch another attack).
The speedy pre-battle stealth isn't far off from what imagined the original MGR would have as its foundation. Yeah, it's not remotely deep, but it feels great grappling around picking off five mooks without a breath in-between.
It's just a really well made game.