From my very limited experience in maya, i can tell you that polygons are basically flat surfaces connected to each other. connect enough polygons and you get a "smooth" curved object.
They are very easy to work with and are good for modeling inorganic objects.
NURBS are curve based surfaces that are less intuitive but better for modeling organic surfaces. They also take more time to calculate and take more juice out of your computer.
SubD's are some kind of mix between nurbs and polygons. They are like polygons, only, better suited to organic models.
hope that's any help.