It really depends on the particular job and very much so on personal preference. Some people only like to model with nurbs & subds, others only like to use polys and (I'm guessing) most people use a combination of the three, even on the same project at times.
my question is which tool do i use to create things like human body and cars , things that have alot of curves.
Nope, that's correct. Polygons do have a little more to offer in some areas than nurbs do - HOWEVER, nurbs absolutely kick backside when it comes to making a nice smooth-flowing shape with smooth transitions in curvature, which is much harder to achieve in cases with polys.
when i use NURBS surface i cant combine it with polygons and other NURBS surface , its like i feel that NURBS surface is lacking some functions that polygons offer. EP curve produces NURBS surface , am i wrong?
It Certainly is. By making use of the split poly tool, extrude edge, extrude face, bevel, tools (amongst the others, obviously) you can create some amazing stuff. Much like anything - a huge amount of it comes down to experience, knowing how to tackle each individual aspect of a model/project. As an example, I'm less than useless at modelling cars, so far - I've just not done enough of it. But give me a person and I can make something that only half as many of you will laugh at, in next to no time.
so issit possilbe to sculpt from a raw polygon shape ? pulling vertex and stuff