By feats Isshou wins. He created GIANT METEOR SHOWERS for fun, while eating. To be honest Fujitora is probably the strongest Admiral so far. He can bend Light to his will (thus annihilating Kizaru) and because Ice is brittle he can annihilate Kuzan tooBy feats obviously akoiji
But if anything akoiji and akanu should be close in powers (they fought for 10 days) akainu is above current admirals (maybe not kizaru but he's getting really old in 60's now) akoiji if he had any similar development like akainu did then he should still defeat fuji
But logically fuji and akoiji should have same level of Haki and logically fuji's devil fruit powers should beat akoiji's
Gravity> ice but then again akoiji has more mastery over it ...... So yeah akoiji but he most likely loses another limb but fuji loses his life lol
Isshou clearly has the best haki anyways, he lives while using it permanently.