A line graph would be best for emphasizing the overall pattern of membership trends over the course of the year. A line graph also allows for easy comparison of Eastern and Northern categories.
The best graph for comparing total membership to categorical subdivisions depends on the type of quantitative relationship that you want to highlight. A stacked bar graph could emphasize the part-to-whole relationships, but it becomes too cluttered with four subcategories and 12 time points for each. Reducing this to 4 time values, as others have suggested is a good solution.
If the time series relationships are most important for interpretation, a line graph could be used to emphasize the overall pattern for each subcategory. With this dataset, a clear pattern emerges that also allows for ranking.