Hmm. I don't know if the 3rd is dumb, but we don't know if he'd be smart enough to figure out Pain's secrets either. Just because he's brawny doesn't mean he's unintelligent.
If it's the Six Paths, then Sandaime Raikage wins but only if he can dodge large scale Shinra Tensei (not impossible with his speed, he'd just have to jump REALLY high into the air).
Well, actually no. Nevermind. We do not know, and can only assume that he has long-range ninjutsu to take out Chibaku Tensei. Plus we cannot assume that he is smart enough to know to attack the orb.
Only Itachi knew that, obviously. Or a lot more ninja would have survived against Pain.