Tested different kinds of Algo coins.

CPU: Intel(R) Core(TM) i5-4570 CPU @ 3.20GHz
System: windows 7 64-bit.

http://www.cpu-coin.com/wp-content/uploads/2014/06/CPUMiningComparison.png

CryptoNight algo coins' power-cost is lowest in all of them.

More info from - www.cpu-coin.com