I think it depends on a few things:

Is your kettle electric or stove top? If stove top, is your stove gas or electric?
Gas stove top w stove top kettle is more energy efficient than boiling an electric kettle (strange but true!) if you fit the burner size to the base of the kettle, ie small kettle on big burner is a no-no.

If you have a gas stove top and you put a lid on the pot, match the burner size to the pot size and use the same amount of water you would have put in the kettle anyway, doing it in the pot will be equally as efficient as using the kettle.

There is absolutely no need to boil the kettle prior to making rice in the microwave, that is excessive