Neither. They'd probably fight for a while, realize they have common goals, and make a heck of a crossover on FanFiction.net in which the universe will divide by zero.
Seriously, though, from what I've seen, they are pretty equally matched when they're both at full strength (Nobody's dead in Akatsuki's case) and the battle would last a while. I'd put my money on Akatsuki if my first theory somehow failed to happen.