I'd have to say, Porsche Cayman GT4.
I've always been skeptical about Porsches prior to GT Sport, what with their whole exclusive deal with EA, and rumours about how they "protect" the 911. I keep thinking all this praise in reviews can't be real, and surely journalists are being paid off to praise the rear engined 911. Sure, the GT3 RS is amazing and all, but I for some reason just never felt an emotional connection to it. Even though it's able and stable, there was always that fear at the back of my mind. I was always acutely aware that I'm driving a RR car with way too much power for anyone's good. I would always hold out that last 2% on a track as a result.
The Cayman however, is predictible, compliant, easy to see out of, and sticks to the road like glue. It holds the title of "Handling Nirvana" in my head for this game. I actually think it is the perfect sports car; it's a hell of a looker, sounds unmistakable, iconic, and pleasant. It handles like a freaking dream and makes me smile and try stupid things I shouldn't whenever I hop into it. It's an experience that simply doesn't get old. It's a sports car you could feasibly live with, and wouldn't be embarrassed to drive to a first meeting with your hopeful future in-laws. It doesn't pretend to be anything it isn't, nor does it cater to a wide audience. It offers the beautifully focused, pure driving experience I love in Vipers and RX-7s, except with the marketing and power to make the whole package work.
Granted, the only Cayman in GTS thus far is the GT4 variant. But if the production car is even a fraction as good as the GT4... ohh boy. Yes, BoP hasn't been kind to it in Gr.4 category. Yes, it has gears WAY too long for its own good. But it's one of the only two Gr.4 cars that exist in real life, and it's a crying shame that, with all the fictional Gr.3 and 4 cars being based off on existing production models, we don't get to sample a production Cayman.