I'd say Crisis of Infinite Earths is hands down the winner in casualties.
Zero Hour (kind of IIRC) and Infinite Crisis reignited the Multiverse so it was more of a resurrection of trillions :P
The crisis usually are cosmic doomsday scenarios that would simply end the world if it had not Superheros. So the death toll is usually between comparable to significantly higher than that of our real-world disasters but everyone is still happy because its either that or all are dead. Simplified spoken. The survivors of the COIE where not really happy; but their minds and sense of reality got reset so it did not really matter for them anymore anyway.