When I think of custom, I think of a vehicle that has been heavily modified in a way that it cannot easily be returned to stock. Like the Cuda on here that is being channeled or the extensive floor pan mods that were performed on the Sick Fish. These are true customs. Most modified drag cars also fall ito this catagory with back half suspension systems and modified interior tin work.
Everything else is a just a bolt on to a stock platform, imo. Even the XV stage 2 stuff, which requires minor cutting and welding, is not radical surgury and can be reversed. To call a car custom because it has a billet alternator bracket or non original wheel and tires sizes, as is apt to happen in big show judging, is kind of a cop out to me. It is still the original platform all those niceties are hanging from.
In that frame of reference, I'd say stock because a true custom entails considerable modifications which most aren't inclined to tackle.
The G-machine look is also kind of subjective to me as well. Much like Pro Street became a charicature, some have taken the G Machine look to a level of silliness. I'm all for big tires and lowered stances, but 20-22 inch rims with air ride suspension just so you can park the car on the ground seems silly. It's kinda like triple D cups on a 5" tall women. It is intersting enough to look at once or twice, but I wouldn't want to live with it day in and day out.