Difference between Members Directory and Blog Directory

I know this question has been asked before, but I need more clarification. I currently have the members directory installed where all new blogs are members and therefore in the directory; what would be the difference with the blogs directory? We have a couple of different blog types that include personal bloggers, businesses, organizations. Right now the members directory puts them all together. I would like to have the ability to list separately; would any of the other directories provide this ability? What would you recommend?