Who should I rank up? 4* Duped r4 Medusa, 5*non-duped r2 Medusa, 5* non-duped r2 Vision Aarkus

MCOC_JCM

Currently trying to finish Act 4 100%

Chikel

5 star non-duped Medusa

5* Medusa. You only need her sig ability for AW defense in low tier alliances.
Vision Aarkus is also good for both defense and attack but Medusa will serve you better.

Thicco_Mode

5 star non-duped Vision Aarkus

If your focus is act four 100%, I think aarkus is better because he has more damage. medusa is more useful overall, though