hey well from what i can see is that nurbs are for organic modeling such as ppl, animals, etc. and polygons are for modeling inorganic modeling like inaminate objects-- rock, table, etc.
also from what i can see is that nurbs take up more processing power but are better for animating and bending
subdiv surfaces are really more of a mix between the two
u can use subdiv surfaces if you want it all really depends on what you plan on modeling and how you wanna model it ----check out the "free" dog tutorial in the video training page it shows you a little bit about the differences