GINN > Zaku on an aesthetic level, Zaku's use and Axe and big bulky shields, kinda like barbarians, GINN's use nifty swords and are more elegant and seemed more graceful. And once the war is over, it's always the pretty weapons that get glorified no matter how much violent death they caused.

NOTE: Talking about battle ownage potential is pointless since any intelligent military wouldn't roll out something new unless it was significantyly superior to what it's replacing. Ttherefore zaku's are most definately better suited for the jobs that they are assigned than their older counterparts