I find the Gran Coupe the much more beautiful car. But the Panamera is I think more exclusive. I drove the 640d Gran Coupe already and also the Panamera diesel and the Gran Coupe wins big time. 313 BHP against 250 BHP, rear wheel drive against front wheel drive even the handling of the Porsche was not Porsche like! The same goes for the basic Panamera although it handles much better than the diesel Panny.
But the Panamera 4S is a totally different ballgame. This car is a full blood sports car and you cannot compare it with a Gran Coupe which is a GT car! I haven't driven a 650ix Gran Coupe so I cannot compare it with the Panamera.
For a everyday drive I would pick the Gran Coupe myself.
Good luck with choosing, you cannot go wrong with one of these cars
