Answer: Neither is efficient. Electric heat that is produced by the process of "electric resistance", the red glowing elements we are all familiar with is the least efficient way to produce heat known. It is always the same efficiency with one BTU of heat produce for each watt of energy used. For this reason, electric resistance heat is used as a baseline of comparison for the efficiency of all electric heaters including heat pumps. When a heat pump is rated with a Coefficient of Performance (COP) of 3.5 that literally means that it delivers 350% more BTU's of heat per watt used than an electric resistance heating unit will! The units you describe vary only in that one uses a fan to distribute the heat and the other uses oil as a heat sink to absorb the heat produced by the elements and then release it by convection and radiation. If you have no other option but electric resistance of course do it, but if you have any other option, look into that.