it realy depends on what u want to achieve.
I prefer nurbs, but i have to say that using polys it is more easy to evaluate the shape of the car body.
If u have the overall shape of the car body modelled with nurbs (this can be a hard job) it is VERY easy to integrate finer details like holes, corners etc.
but since this forum is mostly used by game modellers it is clear that the poll shows polys as the best way to go
nice day
C.