Answer:
I would say nuclear and/or other renewable sources such as hydro, solar, turbine.
Step-by-step explanation:
Nuclear is the cleanest source of energy out there, and is one of the more efficient ways of energy. However, nuclear energy is also the riskiest. Events such as Chernobyl are examples of the dangers of nuclear power plants. The radioactive effects of a nuclear power plant detonating is long term and causes quite a bit of damage ecologically, biologically, and economically.
If it werent for the risk factor nuclear would be the best way of energy by far.