polys are easy and they do give sometimes a very impressive result.... nurbs are a bit more complex but they are good too.... i use nurbs for modelling cloth, for ex.. a bedsheet... just create the curves and loft em(which takes hours on polys).... and other stuff like a house etc..... for character modelling i use sub-ds....
it actually depends on what you are modelling.... well, everyone might not agree with me on that... but most of the time i use polys.