Hi Felix,

> From the little I know, quads seems to work better
> with the Catmull-Clark sub-d method.

It's not just simply having quads - to get good subdivision results also requires a suitable topology.

There are all kinds of bumps and wrinkles and artifacts that can be caused by poorly suited topology being used for sub-d, see this video for a good overview of that:
http://vimeo.com/2158706

That video covers a variety of sub-d smoothing artifacts, and how to best arrange your input mesh structure to avoid them.

If you want to produce sub-d smoothing, your best bet is to create the mesh for it by hand, following a strategy that produces a good sub-d friendly topology. It's a whole different modeling process than building stuff in MoI and exporting an n-gon mesh.

- Michael