The most energetic electromagnetic radiations are
Gamma rays
The different types of radiation are defined by the amount of energy found in their photons.
Radio waves have photons with low energy, microwave photons have a little more energy than radio waves. Infrared photons have still more, then visible, ultraviolet, X-rays, and, the most energetic of all is the Gamma-rays.
So, Gamma rays have maximum energy hence they are the most energetic.