I'd give a massive tl;dr of each of these but basically these are designs for the robot animu idea that I'll never get out of my head.

L-to-R
JKE-4, ZAT-Gamma, JKE-5, Durandal (the "hero" mecha), JKE-6

tl;dr - the JKE-4 is the old design that's everywhere in the star system, the ZAT is the "bad guy" grunt, the JKE-5 is the "good guy" grunt, the Durandal is the Gunbuster (the super robot in an otherwise-real robot world), the JKE-6 is the Sizzler (the powerful late-series unit made in the image of the "hero" mecha).