Old question and very debatable, But I'd like to know which of these locations do you perfer? Guess the PlayGround Games and Turn10 studios would also be interested to know the answer!
Japan, like Australia and the United Kingdom, is right hand drive. It has a mostly cold climate with clear skies and short summer. The cities mostly have narrow streets, I read someone said that "I've been down roads so narrow I had to fold my wing mirrors in - in a mini-car.".
California has big roads, is left hand drive - which is common for most of us!, it is warm and "summery". Though, some places of California does snow.
Your vote: Japan!