Best way to throw a round kick for MMA and instructions on how its done?

There are so many variations on this kick, so can you tell me the variation thats gonna be the most useful? / Is the most powerful/ Is the most...

Source: http://www.mmaforum.com/standup-technique/104679-best-way-throw-round-kick-mma-instructions-how-its-done.html

Oscar de la Hoya Matt Hughes Mirko Cro Cop Rashad Evans