Answer is from coal and from oil again.
And the winner is nuclear power with all their pollution and possible horror accidents..
Don't count on power of sun and wind , this is small percentage even now.
Coal power is the most polluting form of energy ever invented in the history of the human race. You can travel to the tier-II cities of Russia and Ukraine, and experience the pollution yourself. In cities such as Konakovo, Kirishi, Nazarovo, and Sharypovo, the pollution is so intense that sometimes it is impossible to see the sun, even during daytime.
In my opinion, nuclear energy is the cleanest form of energy.
It is the cleanest but is it the safest? What to do and how to deal with it if some incident happens, how can that be avoided? I'm a bit scared of nuclear energy but that doesn't mean that I'm against it.
Would you really say that it is cleaner and safer than solar? I don't see any energy source cleaner or safer than solar, though wind might be close.
Fusion!
Longterm it is cleaner and more efficient. But right now we need better methods of creating ultra strong magnetic fields.