I say Akatsuki, very high diff. Most of them are being seriously underestimated here, though the Kage definitely have some major players. Hashirama, Third Raikage, Mū, and many others will be tough for Akatsuki to deal with. However, I think Akatsuki have the wider range of abilities, and a better teamwork factor if this is IC. Sasori and Deidara, for instance, worked together well, so did Hidan and Kakuzu, though both argued frequently, Hidan and Kakuzu were effective enough to easily smack around Asuma and his team, with their only saving grace being Shikamaru's intelligence. Hidan alone would have easily taken out Asuma, but that's besides the point.
A number of the Akatsuki are being underestimated, here. I wouldn't say any of them fodder, especially not Sasori and Konan, saved for Hidan, who definitely goes down quicker than the rest. It'll be easy for even one of the Kage to cut his head off, thus either distracting Kakuzu or leaving Hidan incapacitated. If this is IC, Kakuzu is more likely to just ignore him and keep up with whatever fight he's participating in. Karin probably goes down quick, too, with her only real offensive jutsu being the chakra chains, which might be useful early on. If she sticks on the side, though, and manages to avoid attacks, she's a powerful healer, and can help out with strategies using her sensory abilities.
Suigetsu and Jūgo are painfully underestimated as fodder. Suigetsu's water jutsu are powerful for both offense and defense, though certainly not Kage-level. Jūgo, once he activates his 'darker side' like he did in the Kage Summit fight, is a powerful and brutal fighter, though he did fodder against the Raikage. Put either of them on support for one of Akatsuki, a good tank like Kakuzu or Kisame, and they're great support for the stronger shinobi. Eventually, one of the two will get caught in one of the Kage's more powerful jutsu, with Suigetsu probably going down to either the Third Raikage or A, due to their lightning jutsu. Still, there's potential for the two of them to get taken out quickly at the beginning of the fight, but since the Akatsuki have some great strategists on their team (Kakuzu, Itachi, Sasuke [if he's in the same mindset as he was during the Deidara and Itachi fights], Nagato / Pain, Orochimaru to a degree, even Sasori and Deidara to a lesser degree) I doubt they'll be on the forefront of the battle where they can get easily picked off.
On that note, if Hidan is kept nearby Kakuzu, he's more likely to survive longer. The two were considered unstoppable together, though that's note true as some of the stronger Kage (Hashirama, Third Raikage, probably more) could undoubtedly solo the two of them, and fight better as a team than their bickering lets on. However, Akatsuki has some real idiots on the team, notably Hidan. He might rush in and get his ass kicked early, making him a moot point. If he doesn't, though, and he gets some Kage blood in the battle, well that's a few Kage down from the get-go.
Sasori is horribly underestimated if you consider him to be fodder. Having taken down the Third Kazekage, he's easily Kage-level and most likely the single most powerful shinobi to ever come out of Sunagakure. Sasori's jutsu actually gives Akatsuki some of the greatest advantages in the battle, if he starts out strong rather than building his way up. Forgoing Hiruko, who would be absolutely useless against any of the Kage, Sasori could start out with the Third Kazekage puppet's Magnet Release jutsu, poisoning some of the less quick Kage from the start and leaving them prone to be easily killed by one of the other Akatsuki. Sasori works best in a group as support, I think, since his jutsu are very unique and predominantly long-ranged. Sakura and Chiyo got the jump on him mostly because they were close-ranged experts, certainly not a good match-up against a puppet master like him. Once Sasori gets to the point of his puppet body and the 100 puppets? He gives the Akatsuki a major numbers advantage, potentially overwhelming the Kage. The puppets themselves will be easily taken out, but to do so the Kage would need to focus their attention onto the puppets, giving other Akatsuki members openings to take some of them out. This goes on for over 100 puppets, since Sasori is noted to have just under 300 puppets in his possession, and all of their weapons are poisoned. No matter which Kage it is, if they get so much as a scratch on them, it's pretty much all over for them. Sasori himself is no slouch either, with his fire blasts having enough intensity to burn through rock and his extremely fast cord poisoned as well. Sasori definitely doesn't fodder, here.
Hashirama is a huge problem for Akatsuki. He's called the God of Shinobi for good reason, and his Shin Sūsenju will be absurdly difficult for Akatsuki to deal with... but this Akatsuki has Obito, Pain, and Nagato, three Rinnegan users, though Obito isn't shown using the Rinnegan's jutsu often. Pain and Nagato, at least, have jutsu that could at least keep the statue at bay (Deva Path's gravity jutsu, Asura Path's arm cannon and possibly missiles, Animal Path's enormous summons from both of them). Plus, there's Gedō Mazō. Three of them, unless only one can be summoned. That puts Akatsuki at a severe advantage, plus Obito has the Jinchuuriki on his side, possibly giving him access to six Tailed Beast forms. That's an incredible amount of power, if all focused against the Buddha, and many of Akatsuki, Pain and Nagato especially, have access to powerful Fire Release jutsu. The Buddha will be tough to take on, absolutely, but I don't doubt the Akatsuki can do it with just the three Rinnegan users.
Zetsu probably fodders, if he doesn't play it carefully. If he does, he could be an extraordinarily useful ally, popping up from the ground and using a quick Wood Release jutsu before returning to the ground and appearing elsewhere. It would be a good tactic, but whether or not it would happen is debatable. I'm just going to assume he fodders early on, considering how powerful and fast the Kage are. Even with that tactic, Minato or A could easily use outspeed him and kill him early. So, yeah, Zetsu is pointless here.
There's also this point: Three of the most skilled Uchiha on the Akatsuki, none on the Kage team. Though Danzo does have ten Sharingan, he doesn't have nearly enough skill with it to match up with any of the Uchiha in Akatsuki, considering the amount of times Sasuke killed him during their fight, and how desperate he was near the end... when Sasuke wasn't even close to exhausted. Danzo is honestly kind of useless in this fight, if you pit him against the right person. Sasuke alone would do nicely, as this is EMS Sasuke who is well beyond the MS Sasuke who fought him before, and Itachi would certainly take care of him. Plus, Itachi and Sasuke both have MS, giving them Susano'o and all the other powerful jutsu that come with it. Itachi's Susano'o, especially, will be able to seal some of the more powerful Kage away with just a stab, if he plays his cards right.
Konan's prep time, combined with full intel, was probably one of the best things Akatsuki has going for them, here. The way she nearly killed Obito, with the only thing saving him being plot armor, was incredibly impressive. If she has knowledge of all Kage, and the time to prepare jutsu specifically to take them out, she easily makes up for Zetsu and Hidan's slouching.
This is already a long enough post, though. Orochimaru and DSM Kabuto are extremely powerful and often underestimated, Kisame has some of the strongest water jutsu in the series, Kakuzu and Deidara are absurdly powerful when you take their abilities into full account... Though it will be an extremely tough fight, I think Akatsuki would ultimately win. It really comes down to the strategy on the two sides, I think, and we've seen more of Akatsuki's strategists than the Kage's... so, yeah. Akatsuki extremely high diff.