We had a 1968 GT 500 stick, in the '80's. Couldn't really afford to keep her.
I still like the 67 styling cues over the 68
The 68 steering wheel and wood grain interior were not as appealing, to me.
The 67 door panels are nicer, and I like the head-light treatment better.
Aside from the side clearance lights, most everything was the same
except the 68 had the (nicer) sequential turn signals
Engine wise, the 67 came with 2/4's on the FE, the 68 came with 1/4bbl on the PI engine and also on the KR
The 2/4's had the cooler looking air filter assembly
Asking someone which car is better, is like asking someone which kind of beer is better.
Making a long story short, the gentleman which we sold the car to, many years ago, did an amazing job bringing the car back to original condition