Hi Peelman,
For ArchiCAD users it would be preferable if it was supplied as a .gsm file which is the standard ArchiCAD library part format. This would then allow you to add parameters to choose between different materials, or display different options available for that piece of furniture (for example - the number of shelves). You may find you need to know a little GDL coding to do this effectively - I don't know if you would want to get into this.
The next best option would be a .3ds file. ArchiCAD has the facility to convert these into .gsm objects, but you will lose a lot of the fine parametric control that you could have added manually. See this site for examples of .3ds and auto converted .gsm files.
http://www.archibaseplanet.com/
One of the complaints about the library parts from that site is that they are too polygon heavy for ArchiCAD to handle. Many have over 40000 polygons! Typically, anything over 5000 is considered excessive for a single object. Under a 1000 is preferable. Other programs seem to be affected less by high polygon objects, and can actually get better results when rendering from the extra detail provided, so in an ideal world you would provide a lower poly version for use in ArchiCAD, and a higher one for other rendering programs.
A 3d .dwg is another importable option similar to .3ds.
Hope that helps.
