I tend to find the other energy types to be fairly mundane or boring. However, electricity is wild and random and powerful and really comes across as something other than mundane. I envision a lightning bolt streaking across a battlefield, an iconic vision when it comes to fantasy. Electricity is not something a person can do naturally and thus it squarely falls into the realm of fantasy. While such things as cold or sonic are also something a person can normally do, they lack ooomph and power. Electricity is where it's at!