To determine which American cities are the most exciting in which to live, the least biased and most useful sample would be citizens from each city in the running. This option ensures that those providing feedback have direct experience living in the cities being considered, leading to more relevant and informed opinions about the excitement of living there.
The other options, such as groups of foreign tourists or political leaders, may not have the same level of insight or lived experience in those cities, and citizens from various cities would not provide specific feedback about the cities in the running.