This is my favorite way for car modeling.
First I'm using MoI (a NURBS modeler) to create the basic surfaces. This has the advantage of producing nice curvature on surfaces. However it's not easy to "stitch" different surfaces together without gaps.
So then I import the model into MODO where I "skin" over the underlying surfaces with regular quad polygons. I use MODO's snapping features, forcing the polygons to stick to the underlying model, and finaly I turn-on SubD to make it smoother.

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