If speed/DOF differences are of no import, I would always go for the macro lens, as it is more versatile. For a time, I used the Canon 50mm f/2.5 macro as one of my standard lenses, and was very happy with it at all focusing distances.

This being said, the 105 2.5 is an outstanding lens, and they are plentiful and cheap. If putting extension rings on will not a a big hindrance to you when you are shooting, I would just save the dough and pick up on older one (pre-AI if you have a pre-AI camera, or AI if you don't).