>> Another advantage of OBJ is that it support quads. I think 3DS only 
>> supports
>> triangles?
>
>  Rendering a (non-rectangular) textured quad is not an unambiguous 
> process.
> How do you do that? Dividing it into two triangles will get you a 
> texturing
> artifact.

To be clearer, there is no expected or obvious way how the inside of a quad 
should be textured given the four vertex texture coordinates.  Converting to 
two triangles does it one way, but there are other possibilities.  In 
practise every modeller and renderer will convert it to two triangles, so I 
guess that can be thought of the "standard" way.

However, a more fundamental problem with quads is if the vertices are 
non-planar.  Now, depending on how you triangulate it, you will actually get 
different geometry.  For this reason, when you model using quads you should 
try to keep them as close to planar as possible, otherwise you might be 
surprised at the output, or when you come to smooth the mesh you will get 
some funny results.

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