It depends on the differences between any styles you make. Take here for instance - we style for clients on this site, so each style is separate and not used as a child style because they're all built different ways. If you're using the same format for all of your styles and simply changing the colours, then yes - make them all child styles. If each one has a different look and requires different template edits then I would recommend not using child styles of the default.
Also with the plug in system vb now uses, it's much easier to upgrade sites and styles quickly and efficientiy
oh... and well done on your first post
