It is difficult to say which source of energy is the best on Earth. THe decision is subjective. You can answer - which form of energy costs the least or most as on today. In future some form may be more expensive than other, one may not be available as much as another.
Nuclear fusion energy is available abundantly, it is easy to generate this energy. But used radioactive materials are radioactive for a longtime. So there is some problem of safety for public. The nuclear energy can last for long long time.
solar energy is source available abundantly. It seems to be expensive at the moment. It is limited by clouds, rains sometimes. But it is a safe process . it is a renewable energy. FOr a long time it is available. It may become economically viable in future.
hydel projects - generating electricity from water flow (kinetic energy) in rivers, is also a good source. But there is not enough power throughout the year. In summers, the rivers may not flow at high levels & energy.
Thermal energy is perhaps available right now and used a lot. But causes some pollution and uses coal which may deplete in some years.