Hidan, imo
Zetsu is smarter, can bind him with Mokuton, has no blood, can fuse with the land, etc.
He's not really weak, but rather just featless. Saying that he's weak would be the same as calling Tobirama weak.Yahiko, we know nothing about him other than that he performed a Suiton and died from a Kunai -_-
pain is weakest .