There are a few things missing from your question, which make it hard to answer well.
* what is your maximum budget
* what applications do you need to use
* what sort of complexityofmodels will you be using
For 3D modelling, you also need to think in terms of supported drivers and supported hardware for particular modelling packages. No point in buying a particular GPUif the package you have to use won't support it.
Comparison of three different Quadro FX mobile chipsets here - note particularly the graphic memory bandwidth:http://www.nvidia.com/page/quadrofx_go.html
or, to compare with other models in more detail:http://www.nvidia.com/object/IO_11761.html
You might find these discussions useful:http://www.archinect.com/forum/threa...d=40280_0_42_0http://discussion.autodesk.com/threa...hreadID=467636http://www.highend3d.com/boards/inde...owtopic=223080
and this performance benchmark table:http://www.gamepc.com/labs/view_cont...ookie%5Ftest=1
remember that your GPU is used for the modelling and low-quality but interactive rendering (wireframe, flat, gouraud and phong shading) while your CPU is used for high quality rendering (radiosity, ray-tracing).
Sumary - it depends. However, since you asked what 'the best' was, then the Dell Precision M90 looks like a solid choice and arguably the best currently available in a laptop.