I think that a line graph would be best for sharing membership trends over the course of the year as it can depict the ebbs and flows easily. If i was graphing total membership vs employee/spouse/dependent, i would switch to a bar graph with different colors to show which bar is higher/lower than the others more easily. To show eastern and northern on that same chart, I would have those regions on the bottom, and then each bar on the bar graph would be a different color for each type of membership.