Gas is more efficient than electric element hot water heaters. But, both of those electric and gas will not come close to microwave technology. Microwaves do not consume as much electricity. Again they are not even comparable can you come up with something better please
Actually, that's quite not true. That is something that varies from country to country. Take Brazil for example. The electric instantaneous water heater market is very big in Brazil. The reason for the preference of electric boilers is because electricity is cheaper than gas in Brazil.