I'm going with Sai b/c of his high knowledge of the battle field being an ANBU and all, Great swordsmanship and that one big move he did against Zombie Deidera
Kimi would need to get close to sai or hit him with finger bullets or young ferns ( his forest of bones he can merge with ) but I don't think sai has ink jutsu strong enough to hurt kimimaro let alone kill him, his bone KG is 2 strong he can cut through ink beasts easily.