In the opening of the film 'Overview of America', by the John Birch Society, a rather remarkable claim is made. The film stated that the United States has developed 'the finest governmental system ever devised by man'.
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This is an extraordinary claim as most democracies in the world have a parliamentary system which is widely regarded as giving better systemic accountability and being more democratic than a presidential republic in the styles of the US.

Separating the Head of Government and Head of State which occurs in parliamentary system makes the executive directly accountable to the people's representatives.

The democracy index lists countries in order of freedom and democracy:
http://a330.g.akamai.net/7/330/25828/...

In the 2008 list, 18 out of the top 20 countries have parliamentary system and only one (the United States) has a presidential system of government. At the other end of the scale however, 5 out of the 10 least free and democratic countries have a presidential system and none have a parliamentary system.