Which part of the Earth receives most of the Sun's energy?

The answer is easy - that part of the Earth where the Sun is DIRECTLY OVERHEAD at mid day.

However, the answer is also complex because this point moves on a daily basis between the latitudes of the Tropic of Capricorn in the Southern Hemisphere where it is overhead on or around the 21st December the southern "solstice" and the Tropic of Cancer in the northern hemisphere where it is overhead on or around the 21st June the northern "solstice". This movement is caused by the tilt of the Earth's axis of spin by 23° 26′ 16″ to the plane in which the Earth orbits the Sun.