5. Audi A8L Remetz Executive (used by the King of the Netherlands, Willem-Alexander)

4. Lexus LS460L (used by the Prime Minister of Singapore, currently Lee Hsien Loong)

3. Toyota Century Royal (used by the Emperor of Japan, Emperor Akihoto)

2. Jaguar XJ Sentinel (used by the Prime Minister of the United Kingdom, currently Theresa May)

1. Bentley State Limousine (used by the Queen of the United Kingdom, Queen Elizabeth II)

May be SLIGHTLY biased with that last one, but whatever.