Kizaru for sure.
Him going down (at least temporarily) to a single clean hit from G5 is not something probably even the biggest admiral haters would've predicted.
It looks even worse when we see that Lucci was up in a couple of mins after getting downed by Luffy, and he took like 3-4 hits. Granted this attack obviously should be a lot stronger than the one Lucci took, but still..... the optics is horrible here.
With what we have seen now, IMO Kaido would need high-diff at most to defeat Kizaru. While earlier, I used to think it was high diff at minimum and possibly extreme diff. I also used to scale Kizaru above Luffy.
With Sanji, at least we don't know how Saturn's power works, how we scale this, etc.