For me it's Sekiro; Ghost of Tsushima is also great, but once the Sekiro combat clicks it feels completely different.
The sword combat in Ghost of Tsushima is undoubtedly the most fun, but it isn't very challenging unless you're in lethal mode. Overall, Sekiro is the best, in my opinion.
I would say Sekiro has the best combat system.
Brother, KCD and Sekiro are leagues ahead unless you're on lethal mode, because most of the time you don't feel any threat in Ghost of Tsushima.
It's an extremely average game.
KCD offers the most realistic and satisfying sword fights.
Sekiro!! Period.
That might be Sekiro.
Sekiro.
No competition.
Sekiro, Sekiro, Sekiro.