Is it cheaper to use a plug-in oil radiator to heat an individual room, or run the central heater to heat an individual room and living room?

With winter coming up, I have two options for home heating.

Central unit

• I can use the central unit and close/open vents throughout the house to heat up only the individual rooms I want. This would heat up rooms very quickly. However, to make this work, the living room with the thermostat will also need to be heated so that the thermostat reads the proper temperature. The living room is by far the largest space at about 2.5 times the size of the largest room.

Oil-filled radiator

• I can use an oil-filled radiator to heat up an individual room. This would be much slower, but I wouldn't have to heat up the entire living room. However, the oil-filled heater might not be as efficient as the central unit. I don't know. I plan to rarely heat up the living, no more than once per month.

Edit: The central heating unit is actually a heating kit made up of a few coils that is added to the central a/c.

Edit 2: Where I live, it might freeze once per year over night for a few hours.

Which would be more efficient on the electrical bill, and would t be considerable or negligible?