Man, for me, it's Connor and it ain't even close.
That boy was a legit psychopath. Cant blame considering his people were genocided and he watched his mom get cooked alive five feet away from him.
Hell, there was one animation I remember in which dude will legit try to decapitate an enemy. Breh literally hacks at the neck with a tomahawk before finally conceding it aint coming off on some
Connors style wasn't pretty or Assassin like at all, imo, and that was perfect for the character. He felt more like a force of nature. It was angry. Visceral. Savage. He may not have had the skill of an Altair or Ezio, but pound for pound, fade for fade? Nobody would be trying to see dude.