Japan & Germany are a close call. I love Subaru & Mitsubishi, japanese cars are usually very reliable but Germany defnitely takes the cake, I mean BMW, Porsche & Audi >>>
You forgot about Italy (Ferrari, Fiat, Bugatti, Lamborghini)
they make pretty fast cars.
South Korea is trying to improve their game, Hyundai is getting bigger overseas but I think they're kinda regressing in terms of quality & design.
USA can make really great pick ups, but not great compacts. The Corvette ZR1 is obviously their best sport car, the Mustang and Challenger are great too. Citroen (France) makes great rally cars.
The answer is obviously Germany.