The form of your data dictates the form of the map. Raw count data, for example, should not be represented using a choropleth map, since this will yield a display that puts visual emphasis on the largest area units of the map. A choropleth map of the number of cars in southern California, for example, would be dominated by the count of cars in massive (but sparsely populated) San Bernadino County, and would mislead a viewer to perceive that there are not very many cars in southern California. A more appropriate map form for this data would be a proportional symbol map, with circles or other icons of sizes in proportion to their attribute value (count of cars) centered in each spatial unit (county).
This distinction is illustrated in the map of voting results from the Czech Republic. Raw data, in this case total number of votes cast in each district, is represented using proportional symbols, in this case, circles. Ratio data, in this case percent of eligible voters who voted, is shown using a choropleth map underneath the proportional symbols.