There are two ways in which electric heat can be said to be "inefficient." First, there are two ways to generate heat from electricity. You can use resistive dissipative heating, which you are thinking of, or you can operate a heat pump. Heat pumps are more common in cold climates and can reach something like 130% efficiency by taking heat from outside and moving it into the cold house- plus the 100% heat dissipation from electric losses in the pump itself. Compare this to a maximum efficiency of 100% for resistive heating alone. The downside of course is that a heat pump is far more expensive than a resistive heater.
However, electric heating is painfully inefficient when you look at the best solution- directly burning the energy source in the home. Think about it: to get that electricity to run your electric heater, the power company has to burn fuel in a power plant. The power plant efficiency is maybe 40%, meaning the remaining 60% of the heat released during combustion gets dumped into the environment. Then, the electricity must be transmitted over the grid which is only maybe 70% efficient. That means resistance heating, though 100% efficient starting at the wall socket, is less than 30% efficient overall when considering the original energy content of the fuel. Burning the fuel to directly obtain its heat is much better than converting it to electricity to transmit it first.