@Xai:
My personal favourite would be Blood Blood Fruit for Akainu. It seems to suit his foreshadowed personality. He would be a ruthless, no nonsense fighter, who uses blood attacks.
The limitation to the Blood Blood Fruit would be that the user can only manipulate his own blood. He has no control whatsoever on other people's blood. But with his own blood he will be able to do lots of imaginitive things - making "blood" weapons (swords, spikes, daggers, bullets, whatever), making blood mist to impair the opponent's visibility while Akainu can see his opponent clearly in the mist, injecting someone with his blood to control him, etc.
Or, on a more fun note, a Petal Petal Fruit can be hillarious. Seeing a tough s.o.b like Akainu use emo Petal flowers would be so precious1 :P
Actually I think it would be more cool if the blood blood fruit was a Logia type. Way more fitting for an admiral. Though he would be the weakest compared to ice and light.