I'm actually going against the crowd and leaning towards Hebi Sasuke.
Chidori Spear + blossom seems OOC for him to use w/o suitable knowledge on Kakuzu, so it's more of a 1 heart deal, but I'd still vote for the Sauce.
He tanked a C1 explosion with a snake, taking almost no damage in the process.
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With the Curse Mark, he evaded a huge explosion by flying, and tanked another huge explosion by sacrificing a wing.
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Kakuzu's main form of brute offense is a Katon + Futon combo, which would generate
a lot of heat (exactly what Kirin needs to be formed). I do not see a simple Futon jutsu beating something like Kirin, which is a huge jutsu itself. In the end, he still has Manda to assist him so he can focus more on multi-tasking. Genjutsu might be a problem too if there's not an extra heart helping him.
If Kakuzu uses his tentacles to try holding onto Sasuke, he'll have to dispatch them or face Chidori Stream (which would travel through the tentacles too).