Determining which one to use is completely up to you. Here is some information about Group Types which might help with your decision.
http://www.activemodules.com/Commun...fault.aspx http://www.activemodules.com/tabid/...fault.aspx CategoryId under socialview settings isn't implemented yet. That's why in one of the links I provided earlier it shows how to set it up with a custom view.
<active:groupslist runat="server" CategoryId="2" TemplateName="Groups/GroupsList" />