In book III during the arugument, whose fall is worse and why?

God sitting on his throne sees Satan flying towards the newly created Earth. He then shows Satan to the Son who sits at his right hand, and tells him of

the success Satan will have in perverting mankind. God has created man with free will, and the ability to withstand Satan's temptations. And yet he grand humanity grace because his fall is not caused by his own malice as Satan's was, but by the forces of Satan's seduction.

Jesus praises to his Father for the grace he's afforded mankind; but God declares that grace cannot be given to man without the satisfaction of

divine justice. Jesus offers himself a ransom, and is accepted by the Father. God exalts him above all names in heaven and earth, and commands the

angels to adore him; they obey, and hymning to their harps in full choir,

celebrate the Father and the Son.

Satan's fall is worse because he can't change his mind or come back to God. He will never defeat God in His goodness; evil will never win out in the end, as the Son of God has given himself up as ransom for mankind. Satan made a choice from which there's no redemption, but mankind is redeemed through the Son of God.