My bets are on Hiruzen.
When Iruka made that statement about "Prime Hiruzen" he had no idea what Hashirama was capable of, no one did. That's why that leaf shinobi said "so this is how our ancestors fought!?".
Throughout part 2, it's been shown that leaf ninja are aware that Tobirama had space-time ninjutsu. The 3rd was his pupil for crying out loud, he's not going to know anything about the 2nd?