Well, Akainu is a damn tough guy who managed to tank several Haki infused Quakes from WB in the face and was still kicking, while his DF is broken against most of the users, cause even Ace who isw obviously the strongest one here can't protect himself against Akainu's magma, so Akainu is an obvious winner, no matter how hard they try. He is one of the top fighters of all One Piece history, he won't get down against such fodder as Buggy, Nami. Even Fisher Tiger would be a fodder against him, because he as he was before his death was weaker than current Jimbei and it seems that there is quite a differense, because even before becoming Shichibukai Jimbei was said to surpass Fisher Tiger, while after a considerable ammount of time after that he was no match for Akainu at all.
Seriously, the guy can cover half of Punk Hazard in magma and only Ace can fly to some extent, while Buggy needs at least his foot on land, thus Akainu can wipe most of them easily by making loads of magma, the same way he did, when he was fighting against Ao Kiji.
Then, he will only have to fight Ace. This fight wouldn't be as fast as it was in Marineford, but eventually Ace can't harm Akainu that much as well, as Ace doesn't have trained CoA Haki and has lower DF compared to Akainu...