In my experience, its better to smile, do what they say, dont lie, and most importantly dont get agro.
You will come off 10x better than if you try and stick it to the man.
90% of the time you are pulled over because you did something wrong or you did something to draw attention to your car.
Police put sooo much time into trying to nab people for driving offences because it makes money, catching real criminals cost money.