u dnt understand that zetsu can be undetected, if im not mistaken kabuto has been caught and chase out of villages whiles spying when his childhood flashback was going on, zetsu as never been caught while on espionage missions...i knw u like kabuto but he is a human and has human flaws and because has been detected, zetsu can damn near be anywhere he wants since he is connected with the earth and his clonesI fail to see how that's relevant. It's one Jutsu.
OT: Kabuto, easily. He's been successfully spying on the 5 Great Villages and Akatsuki his whole life.