Earth is not a perfect sphere. Its radius at the equator is greater than the poles. Acceleration due to gravity is inversely proportional to the square of its radius. So, the acceleration due to gravity is greatest at poles. Hence, from the relation, W = mg, it is clear that weight is highest at the poles.
We know that the weight of the body is the product of mass and acceleration due to gravity and the acceleration due to gravity increases with the latitude. Now the latitude is minimum at the equator and maximum at the poles So, acceleration due to gravity and hence weight is maximum at the poles and minimum at the equator. Acceleration due to gravity g varies slightly over the surface of Earth, so the weight of an object depends on its location and is not an intrinsic property of the object.