Inertia is a property of matter that is directly related to mass. The greater the mass of an object, the greater its inertia. To determine which object has the least inertia, you would look for the object with the smallest mass.
Since I don’t have the actual mass and velocity values for objects X, W, Z, and Y, I can't tell you which one has the least inertia.
If you provide the mass of each object, I can help you identify which one has the least inertia. Alternatively, the object with the smallest mass will have the least inertia.