Very good points to ponder. If I may ramble a bit...

The 'speed' of the heat could be a race between the air in the duct warming the duct to the point where the heat can be felt, versus the radiator getting a good convection current going in the room.

There may be some heat 'wasted' as it radiates from ductwork into other spaces of the house that you don't want to heat, and a bit more since most circulating fans stop before the heater reaches room temperature, but it is a very small portion.

The central heater seems to have a clear advantage in the electrical service category. The furnace will be wired for the current of the compressor or heater, whichever is largest. However, if you plug in 2 oil-filled radiators rated 1,500 Watts in one room, be prepared for a circuit breaker to trip or a fuse blow unless the outlets in the room are fed from 2 different circuits.

A 120V, 15A outlet can support 1,800 Watts. Several of these can wired to a 20A circuit, which can support a total of 2,400 Watts.

Plug-in appliances are limited to 80% of a 20A circuit, or 16A, or 1920 Watts. At this full rating, they will play heck with a 15A circuit.

I wonder what Mr. Carlton will have to add to this discussion.