This is actually tough, both of them tried to destroy a planet...

I think Aldrich is slighty worse due to his personal villainy.

Yeah slightly worse. Lunaris was willing to destroy the Earth with his own men on it, while Aldritch not only tasked his son on what he considers extreme itself to launch a genocidal takeover on the Earth, gaslights him and grooms him to be a ruthless multiversal conqueror who would cause death and destruction in his conquests, but attempted to destroy the very realm he ruled.

Yeah Aldrich is worse, while Lunaris tried to destroy the planet, Aldrich is mentioned to have destroyed more worlds for their recources, implying that he's killed more combined with attempting to destroy Amphibia alongside the Core makes me think he's a lot worse.