Which is more effective: a U. S. style congressional system or a European-style parliamentary system of government? EXPAIN WH!!!

A parliamentary system or parliamentary democracy is a system of democratic governance of a state (or subordinate entity) where the executive derives its democratic legitimacy from its ability to command the support ("confidence") of the legislature, typically a parliament, and is also held accountable to that parliament. In a parliamentary system, the head of state is usually a person distinct from the head of government. This is in contrast to a presidential system, where the head of state often is also the head of government and, most importantly, where the executive does not derive its democratic legitimacy from the legislature.