Gen6 GT4 FTW
Looks better
faster
Engine is known to be bullet proof so stronger and more reliable
To me then gen6 is still quite modern too, I don't think they are 'old cars' even though in thoery they are if that makes sense. Electric windows, central lockling, air con (some of them) ETC ETC
All depends on each indivitual and what you want in a car.
The running and maintaining costs of the GT4 are exagerated sometimes, if you look after the car and keep it serviced it will look after you for a very long time to come!!!
Fuel prices will affect both cars, obvisouly I would quess your going to use more on the GT4 but I can't imagine the Gen 7 GT been overally great on MPG.
For me its gotta be the 6 but again thats just my view.
Only you know what you want