I'm assuming Madara is not on the other team, because it seems somehow against what I reason is the spirit of the fight: Akatsuki's "traditional" most powerful (excluding Madara) against the rest of "traditional" Akatsuki. I consider Madara something of a dark horse, distinct from Akatsuki.
This is hard to call. Recent events have led me to judge Pein and Itachi well able to defeat the likes of Kakuzu and Sasori, meaning that I've finally admitted that there are shinobi who can put Sasori to rest quite comfortably. He's still dangerous, but I'm not willing to say anymore that he might be able to go toe-to-toe with Itachi. Orochimaru, however, has survived, with yamata and his underground Kusanagi attack synergising perfectly.
Itachi can deal some heavy damage with his Mangekyō, and while he may be a little vulnerable his eventual death won't be the end of the fight: Pein will keep fighting, despite not being as deadly at any one time as Itachi using Mangekyō. The only shinobi I can see being really significant are Sasori, Orochimaru and Deidara. Orochimaru will abuse the chaos to attack Itachi with a bit more common sense, and that's a problem for Itachi. Sasori is deadly, but his enemies know that and have some very powerful and unfair attacks to level at him.
Deidara is similar. C3 #18 and C4 Garuda are very dangerous, which is precisely why Pein will waste no time in attacking Deidara, and why Itachi (who will, with perfect rationality, start with susano'o or amaterasu) will turn to Deidara after using Pein's charge as a distraction to aim for Sasori.
Tentatively I'll say Pein and Itachi. Massive early damage, Itachi dying to Orochimaru (yes, really), and Pein and Orochimaru being precious beauties of invulnerability as the remaining shinobi on Orochimaru's side whittle themselves away ? Hidan and Kakuzu included. Very ilttle will get past Pein's coordinated defences, and Orochimaru will be a stealthy, unfair and tenacious bastard. It'll come down to the two of them, and Orochimaru will lose.