What is the best country on this world?

It depends because most people have different opinions. UN Top 20 countries on the Human Development Index:

1. Norway

2. Australia

3. New Zealand

4. America

5. Ireland

6. Liechtenstein

7. Netherlands

8. Canada

9. Sweden

10. Germany

11. Japan

12. South Korea

13. Switzerland

14. France

15. Israel

16. Finland

17. Iceland

18. Belgium

19. Denmark

20. Spain

source: UN delvelopment report 2010 (wikipedia)