Which ia the best example of potential energy

The best example is when a swing reaches the top of the arc, it has maximum potential energy. Another example is throwing a ball, at the highest point, the potential energy is greatest. A drawn bow also is an example of potential energy.

Explanation:

Energy is the ability to do work. Potential energy is the energy of an object's position or the stored energy (potential to work).

heats surface water up

when two balls of the different masses are dropped from equal height, they reach the ground at the same time .this is because they experience the same acceleration.

the acceleration is independent of mass.

thus when they are dropped they will always maintain the same velocity and travel the same distance (neglect air resistance of course) at the same time.