Question

If all else is constant, which would cause the greatest increase in kinetic energy of a moving object?

Answer 1

First of all there is a big question that what "all else is constant" means here.

KE of a body depends on its mass and velocity.
Moreover you can also say object with bigger mass has large momentum. And body with bigger momentum has greater KE from relation
K=P SQUARE /2M

Or p square = 2KM

Where p is momentum