i acually dunno who to pick because kakuzu has water style to and his only element just isnt fire style, kakuzu has earth release, wind release, fire release, water release, and lighting release. which i could see giving kisame ALOT of trouble considerin electricity conduct to water
so even with the fusion kisame has all kakuzu would have to do is use Lightning Release: False Darkness and zap kisame to his death but thats ninjutsu wise
taijutsu wise all kakuzu would have to do is constrain kisame with his strings just like he did with other ninja that i remember in the naruto vs kakuzu fight and he choked ino and choji rightt? and his sowrd dosnt cut it grinds, and you cant absorb his stings because their apart of him and his earth grudge thing idk
it dosnt seem like it but i say kakuzu wins this one, DONT underestimate the power of earth grudge