Why is fusion preferable to fission?
Fusion is not a chain reaction, so it cannot run out of control as fission can. Any disturbance to the fusion process would cause the plasma in the reactor to extinguish itself. This is a nice built-in safety feature of fusion reactors.
Fission plants can be used to secretly create materials needed for nuclear weapons. It would be far more difficult to do this at a fusion plant, since fissionable materials, needed for nuclear weapons, should not be present at a fusion plant. It would be quite simple to detect the gamma rays emitted by the fissionable matter.
Why is cold fusion preferable to hot fusion?
Brian's
Igloo of Cold Fusion
What Is Cold Fusion?
A Dictionary of Nuclear Terms
Cold Fusion Links