For the purposes of displaying trends in Flores del Mundo’s total membership (Eastern & Northern regions combined), and for showing Eastern and Northern regional memberships separately (but on the same graph), I would use a line graph. For the former, I would use a line without dots. For the latter, I would opt to include the dots to help highlight the differences between the two at each monthly interval.
If we wanted to subdivide the data and show graphs depicting Employee, Spouse, and Dependent enrollment all on the same graph, I might be inclined to suggest that a bar graph would be more effective. The difference between the range of numbers for each subdivision is great enough that, in my opinion, a line graph doesn’t effectively compare the groups to one another. For the Northern region, where there is such a large gap between the number of employee enrollees and the number of either spouse or dependent enrollees, I might even consider using a stacked bar chart. Otherwise, I would consider using a break in the Y-axis in order to effectively demonstrate the trends between the much larger and much smaller values (without having the smaller values appear like an indiscriminate flat line).