[Dr Kain]

Look at the eyes, the snout, the bulge on the top of his head, the teeth. His teeth look much sharper and ferocious on the 89 suit.

And the spines are also the biggest change. The rest of the body looks similar, but it also has to do with the animatronics of the face when you watch the suit in action. There is more life to the 89/91 suit compared to the suits used in 92. 93, and 94/95.

Yes, the suits in Mothra, MechaG, and SpaceG were all different from each other. The differences were subtle, but they were there, with the 92 suit being the worst of all them. It had no emotion at all within the face of the suit and the muscle tone was off.

Here, this might help if you are interested as it explains the differences in detail (such as the legs being bulkier in 94) and there are more pictures.

BioGoji - Wikizilla

MogeGoji | Wikizilla, the Godzilla Resource and Wiki

BTW, I ooopsed. The face shot I gave up right under 94 is actually the 93 one.