It's the best one because it has the deepest and most Complex weapon system. The only soulsborne game I've used all 6 weapon slots in. Main handing a rapier and off handing a curved sword and switching which one you're basing the power stance on is so satisfying in PVP. I'de guess it makes you sick because of framerate scaling or motion blur or something.
I also love it because it's the only soulsborne that rewards "challenge runs" long after the PVP community fell apart I was still attempting no death no bonfire runs where weapon durability actually mattered and the only ways to repair were repair powder and completing a summon. And dying in someone else's world counted as a death so you got to live up to the item description of the small white soapstone.