It depends.  Choose the Plunge Router Attachment when you need to see the complete result of the accessory on the material.  An example would be when you are routing a name or word into a piece of wood.  You need to see what is going on.  If the piece you are working with is small and your interest is in putting a decorative edge on the piece, then your greatest opportunity for success is to keep the tool stationary in the Shaper/Router Table and control the work piece.