no prep , in character , Round 1 - pre time skip , Round 2 - post time skip
Regardless of how you look at it the advantage lies with Kizaru. Look the simple answer is Kizaru doesn't need to be overly powerful. There is a reason why flash can punch and hurt superman even though he is nowhere near the strength of supes and the answer is speed.
Kizaru's power is immensely powerful and assuming that kizaru is a skilled fighter, one can make a successful case for him beating most of the One piece characters.
to answer the topic.
I'll put my money on akianu based on what we have seen so far and here is why; kizaru appears to be a bit of a ditz he lacks both the focus and psychological power to beat akianu. being the strongest or fastest doesn't guarantee a win especially in one piece. kizaru tends to deal with problems in a more straight forward approach thanks to the nature of his power and with akianu's haki, strength and skill i feel that he out clases kizaru is most aspect.