The Pearl Harbor attack was #2, IMO. Although if you count the erdication of the US, UK and Dutch navies in Asia in the first three months of WWII, Yamamoto is unrivaled.
Idiot Biden is boasting about taking out sitting duck Bin Laden, defended with small arms, when it was Bin Laden who was behind what I consider to be the most audacious and innovative and consequential single attack ever executed. The 9/11 attack was asymmetric genius in converting non-weapons (civilian aircraft) into kinetic projectiles and applying the force of those projectiles exactly in places where maximum damage could be inflicted. And the damage was simultaneously military, economic and political.
Audacious, in my mind requires complete surprise thus ruling out Normandy and others where the attack was inevitable and only the date unknown.
To rank high on historical significance the audacious attack must be consequential. This would rule out the Doolittle Raid and Benedict Arnold's slog through Maine to reach Quebec as they were not consequential.
I’m sorry, but the Doolittle Raid was very much “consequential”, in two militarilly applicable (so setting aside the morale impact) ways: first, the Japanese drew a significant number of aircraft and their pilots, aircrew and support personnel back to the Home Islands from the combat zones as a hedge against the US trying something like it again and second it gave Yamamoto the argument he needed for the overreach of Midway.