So here's the deal. As already said by others, the GTO is based on an Austrailian Subsidiary of GM, Holden. In Austrailia, the Holden Monaro (GTO of Austrailia) is regarded as one of the best cars out there. Another benefit of the GTO is its overall fit and finish. Very clean interior, with very nice ammenities. Since its been around, any bugs associated with new cars are sure to be addressed (not likely to be recalled, or have little problems that were overlooked before production). It also has an edge on accessories, since manufactures in Australia are already catering to the Monaro.
So what's wrong with the GTO? Well, the styling is bland, which is both good and bad. If you want to stand out, you better rev the engine, because otherwise at a stoplight, the untrained eye is just looking at a Grand Am. The fact that it is a Pontiac "cookie cutter" style also means the cops won't be trailing you like they would a camaro.
Also, here's something most Ford guys know:
FORD LOVES RACING!!!
Ford is happy to work with their customers, helping them with engine upgrades. GM motors seem a bit secretive. They don't release much information on them, and all current LS1's are hard to work on (look at the camaro, or firebird....the windsheild is a good 2 cylinders over the engine....making it a knuckle breaker to work on.
It's too early to REALLY compare the Stang and the GTO. It's a safe bet that the GTO is better for a family, with a very generous rear seat. But the Mustang is also completely new, and domestic made. The GTO is shipped from austrailia....so true build quality is questionable. Ford has really stepped quality up a knotch. The mustang will feature new technologies, and will yield a lot more accessoroes in the long run.
Mustang exclusivity is basically a joke, at least here in Boston. You can't drive for 5 minutes without seeing 9 mustangs! THEYR"E EVERYWHERE,
I'm personally waiting for hte mustang....it's styling is very nice, Ford's quality appears far superior to GM, and is catching up to the Japanese market's standards (GM cars are notorious for little annoying mosquito problems (PROBLEMS THAT BUG YOU TO DEATH) like their power windows, engine knocking....etc)
Also, the ford is gauranteed to have a ton of accessories, along with aftermarket vendors, like Roush, Saleen, Steeda etc.
THERE'S ALSO RUMOUR OF A SHELBY MUSTANG IN THE WORKS!!!