What do you mean by "efficient"? That word is usually used to describe the fraction of energy that goes into a machine and is then not lost to heat. Since the purpose of a heater is to produce heat, it's pretty much impossible for it to waste energy.
For passive heating, anything puts out exactly as much heat as it consumes electricity; there's no way around thermodynamics to gain or lose power there.
Yes, there can be heat pump systems with e.g. underground connections, and pumping heat can be more effective than generating heat; but for pure heating, generating heat, the simplest resistor heater is just as 100% efficient as any complex electronic device, all the electricity spent results in just as much heat.
