Which type of oscillation would most likely produce an electromagnetic wave?

Electromagnetic waves are waves propagated by simultaneous periodic variations of electric and magnetic field intensity that include radio waves, infrared, visible light, ultraviolet, X-rays and gamma rays.

Damped oscillation means that there is some force that causes the oscillation to become smaller and smaller over time. For example, the pendulum exhibits an oscillation motion. Over time, the swinging of pendulum would come to a stop, unless a force is acted on it.

Forced oscillation means that an outside force causes an object to oscillate at a certain frequency. For instance, if you decide to swing the pendulum so that it won't stop from swinging, the action is called forced oscillation.

On the other hand, resonance oscillation refers to the increase in an amplitude of oscillation of an electric or mechanical system exposed to a periodic force whose frequency is equal or very close to the natural undamped frequency of the system.

Among the three types of oscillation, resonance is most likely to produce an electromagnetic wave.