Who could have the 3rd picked anyway? He picked the 4th, and he died, and he left no one else was worthy of the position. If he had no choice to pick one, he would of pick either Orochimaru, Jiraiya, or Tsunade. But as a sensei he knows all their flaws, and none of them really could become a Hokage. Orochimaru - too ambitious and "evil", Jiraiya - too interested in other things, Tsunade - gambling syndrome. Even the 3 legendary ninjas weren't reliable. Next thing you know...all three of them left the village, so 3rd had no one to pick, and he never knew he was gonna die anyway~