I think Aokiji wins. It's testament enough that of the three admirals it was akainu and aokiji that were slated for next fleet admiral by their higher-ups. Add to that that only after TEN DAYS was there a winner in that match (as a nice reminder of power gaps, compare that to Luffy vs Mingo which has been less then a few hours in manga time)
That's because Kizaru isn't fit to lead the entire Marine force. He can't even remember that a black Den Den Mushi is used to intercept calls, not make them and he's extremely lax, even more so than Kuzan. A Fleet Admiral is just an Admiral with very particularly needed leadership skills, there isn't a gap between Fleet Admiral and Admiral when it comes to power.
OT: I'd give it to Kizaru. Kuzan's ice has always had a degree of transparency, which means Kizaru can just reflect himself through it if he's ever frozen. Kizaru has also shown the ability to pierce through Kuzan's ice. It'd be an extreme diff fight, but I don't see Kuzan winning more than times than I do Kizaru, and especially not by freezing.