The efficiency with which a fuel is converted to heat is only part of the overall efficiency calculation. Consider two natural gas heating systems, one which uses a gas furnace and forced-air system, and one which uses a gas boiler and hydronic in-floor system. Even assuming that the furnace and boiler are of equal efficiency, the hydronic system will be more efficient at space heating, i.e. the kWh of energy required to heat the same house to the same perceived level of comfort will be lower for the hydronic system.
Incidentally, even the fan heater is 100% efficient at converting energy into heat. Frictional losses in the bearings, viscous losses around the rotor, and acoustic noise from the fan blades all end up as heat in the end. Unfortunately, air is a rather poor heat-transfer medium, whether it's in a fan heater, a baseboard convection heater, or a forced-air furnace.
There are numerous factors at work, but I'm aware that this subject is quite removed from the OP's original question.