Four rigid bodies have the same mass and distance from their axis through the center. Which object could rotate easier?

What is the quantitative measurement of how easily a body can be rotated about a given axis?

Suppose a solid sphere and a hoop are rolled up an inclined plane with the same initial velocity. Which object will travel furthest up the plane?

An ice skater spinning while her arms are out. She then put her arms in. What happens to the moment of inertia of the ice skater?