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I have both and can share some experience with you.  The close up lens (especially those two-element ones like Nikon 4T/5T) is very sharp with zooms/short tele without any loss of light.  The magnification increases with the focal length of the lens which is nice. The extension tubes in theory should be sharper but you need to increase exposure to compensate.  You also need more extension with longer focal length.  I usually use the tube with longer focal length (e.g. 180AF) to move closer to the subject.  To get 1:1 with tubes, you will need a lot of extension unless you restrict yourself to standard lens or so.