Hmm The First decides to fight Madara again (and probably win since Madara is said to be weaker now than he was then because of their last battle) while 2nd, 3rd, and 5th throw special kunai everywhere and the 4th takes out the rest nearly instantly with his space/time jutsu because the other 3 useless Hokage's are throwing his shuriken all over the field. Unless of course Sarutobi gets to be young then he could probably do something besides throw shuriken.
We don't really know enough about the Hokages or half the Akatsuki members. Could the 4th just use his thunder god jutsu and kill them all before they realised they were fighting? To many what if's, fun to discuss possible out comes but since we know almost nothing about half of them it all comes down to guessing.
Well according to Kishi young Sarutobi = Yondaime and out of everybody dead 4th is the strongest but there are stronger living people so I'd guess those would be the top dogs of Akatsuki. So Akatsuki would probably be more powerful...But the Hokages (at least 3rd and 4th) would be more skilled, and smarter I'd think. So it would come down to power vs skill. At least imo. Sarutobi probably knows the most jutsu..but that doesn't really help since the old man is being used and he's a weak link just like Tsunade. Which Deidara being the Akatsuki weak link doesn't make up for two Hokage's being weak. So Pein's bodies plus 3 other fighters that could hold their own against at least one of the Hokage's means Akatsuki won't be defeated.
And my first post wasn't really what I thought. Though it would be cool to see 4th beat nearly all Akatsuki by himself it probably couldn't happen. Except the part where a young Sarutobi would probably make the fight a bit less one-sided.