I vote GSX
Why? Well that v6 Turbo GNX can be made real fast, cheap. faster and cheaper than a GSX Stage 1
Unless of course, you put a turbo
or two on the GSX
The GNX is great. The GSX is great now, and was great, during a time when making the baddest musclecar in the land was the goal of the car makers. The GNX didn't have much competition (Monte SS? Yawn. 442 Quad 4? No way)
Put boost into a Stage 1 or Stage 2 GSX and then tell me how the GNX is faster

The GSX is all motor, stock, the GNX isn't, stock. Give the GSX the same advantages of technology and look out
But performance numbers aside, the GSX gets the edge on it's stand-out styling and colors alone. Black is beautiful, it's true, the GNX looks great. It's not eye-catching, though. Everybody has a black car