'sekiro'
As a whole, I would say sekiro with very few doubts: frame rate is more stable, graphics are cleaner, gameplay is smoother and more technical, camera works better, you don't have all those stats that in bloodborne don't work (arcane and bloodtinge are pretty much useless, same for blood gems) but passive and active skills, you don't need to read the wiki to understand what to do, how to do it, and when. Sekiro is more difficult and you really need to learn bosses' attack pattern by hearth and have cold blood to parry their attacks if you want some chances to win, but when you lose you know it's your fault and not the game being unfair (except for bosses' damage output, that's unfair), it's not like in the soulsborne series where camera and gravity are the strongest enemies together with incomprehensible mechanics. Once you get in the right mood, sekiro is fun to play.
Coming to more subjective stuff, sekiro's story is clear, you understand everything and you can even complete questlines without needing the wiki (and to me this is a huge pro), but...
...but bloodborne has its own magic. Setting, lore, atmosphere are something else for me. Lovecraftian inspiration, bestiality versus intellect and how this dichotomy is reflected in the combat system thanks to the regain system is pure genius.
My final verdict is that sekiro is a better videogame in all its aspects, but bloodborne is a piece of art.