The biggest question is whether you sufficiently enjoy the luxury of having the entire dwelling equally warm, or are happy just warming the areas where you spend time.
I live in an all-electric highrise, with through-the-wall combo aircon/heat units. Because those bring in a certain amount of outside air that has to be heated, I've concluded that it's more efficient for me to use plug-in electric radiators in various rooms for most of the winter. I only run the through-the-wall units when I'm planning to use the living-dining room or have company coming.
As I understand it, electric heaters all have equivalent, nearly perfect, efficiency of turning energy into heat. So the difference between my options would be that one is 220v and the other 110v—I don't see how that could make a very large difference in usage—and the issue of introducing (and needing to heat) outside air. I've decided I get enough fresh air introduced from the building's hallway that I'm not concerned about that. Finally, one of my heaters is a radiant type that I use in my home office. It gives me the perception of additional warmth on my skin even beyond what it warms the ambient air to. So I feel like I'm getting a bargain there as well.
In a house with forced-air using ceiling vents, you also have the lost efficiency of ceiling vents (as hot air rises). They make aircon more efficient, but you waste a certain amount of energy warming the air at the top of your rooms, or have to push it downward with a ceiling fan.
