ask yourself which surface will be most suited to creating the shape of the object geometry , for example polygons are more suited to creating straight hard surfaces than nurbs and nurbs arw more suited to creating curvy organic shapes.
It is by no means essential that you use either poly or nurbs for either but simply which you find easiest for you to create what you want .All have advantages and disadvantages , for a newbie though I would suggest you learn polygons as it's really the easiest to master before moving on to other surfaces.