Hidan easy. S-rank level ninja like Hidan won't fall for that cheap silent killing bs. He has shown to have quick reflexes. He blocked Shika's sucker punch. Avoided ninja stars from Asuma from the back. Avoided Shika's shadow throwing the blade at his shadow. I doubt Zabuza's silent killing will work.
Zabuza activates mist. Goes for the silent kill. Hidan reacts and defends the kill strike and tags zabuza. Hidan begins the ritual. Zabuza attacks Hidan. Hidan's superior taijutsu skills wreck Zabuza. No ritual needed.
Zabuza already got schooled by 3-T part 1 Kakashi. The 2nd time they fought, Zabuza was scared shitless and didn't want Kakashi to use his eye. He knows once that happens, its over. Hidan pressured 3 T Part II kakashi with a cordless scythe. Hidan does the same pressure tactics to Zabuza and he'll fold under pressure and die.