Japanese, probably Toyota. Reliable as a wood burning stove, plus they made the MR2, Celica GT4, and of course the Supra.
Europe, everyone loves Ferrari, so I'll say BMW. Good quality cars, nice looking, quick, good handlers, not much else to it.
British, either Noble or Aston Martin.
USA...I dunno. Probably Chevrolet. I like the Camaro.