Hi
In the interests of fuel efficiency:-
An electric kettle is about as efficient converter of power to usable heat as you can get. The type that has the element coil in the water container put all the heat into the water.
Compared to a gas kettle, you get quite a lot of heat wasted as it comes up the side of the kettle.
But don't go out and buy an electric kettle yet - NO if you consider the efficiency of the power generators, they at best can only reach about 40% so 60% of the gas or coal is wasted up the cooling towers etc.
Stick with a gas kettle, but keep the flame small enough to stay under the bottom, your probably doing better over all than the electric.