As far as I know you'd benefit from using a common format for your parser since you won't need to write export/import plugins for Blender/Maya/3DMax/etc because more common formats have those already.

If you go with your own format, you'd have to write import/export plugins for your preferred 3D editor, or a translator as Katie said. Point is, you'll have to create a tool chain around your format to make it usable both for you and other possible users.

But, learning to use an existing library for an existing format might give you some ideas for writing your own (you'd know what kind of functionality you need from the start) so that could help too.

Though I have no experience in these things, I'm exactly in the same section of the arcsynthesis.org book.

As far as I know you'd benefit from using a common format for your parser since you won't need to write export/import plugins for Blender/Maya/3DMax/etc because more common formats have those already.

If you go with your own format, you'd have to write import/export plugins for your preferred 3D editor, or a translator as Katie said. Point is, you'll have to create a tool chain around your format to make it usable both for you and other possible users.

But, learning to use an existing library for an existing format might give you some ideas for writing your own (you'd know what kind of functionality you need from the start) so that could help too.