amon will be superior till satan awakening (10% more def down debuff), she got a hard nuke against raging enemies and mode gauge reduction.

Satan on the otherhand can remove an orb (works against all enemies, not only bosses), has higher burst generation and can buff herself with leech, giving atleast 900hp over 3 turn up to 2700 (unlikely though).

In the long term (awakening august) is satan the better choice.

But listen to several opinions before you decide.