Keep in mind that electric heaters all put out he same amount of heat 1500 watts is 1500 watts, whether it comes from an quartz, ceramic or other heating element. None are going to be significantly more efficient than any other. The ones marketed as "Amish made" (that it turns out were apparently made by the Chinese Amish) Eden pure or life smart are all just expensive hype. I think a good solution is to use a combination of heaters, a force air to heat the space quickly and dry it out (as it moves the air around to pick up condensation) then switch over to an oil radiator as they seem to be able to maintain a more even temperature. The Vornado heaters seem to get generally good ratings and move a lot of air, good both summer and winter. On any space heater I would avoid any that have electronic controls as they tend to default to off if the power drops (common on shore power!) so I would stick to basic ones with physical knobs as controls.
Another good solution is a propane/diesel/wood bulkhead heaters. These will give more heat than electric and each have there advantages and disadvantages. These will need some fans to move the warm air around the boat.
The best solution is to go with a diesel fired furnace/boiler as they will put out more heat than you can get from the shore power line
. If you go water or air is going to depend on the boat layout and how you want to heat the space. Hot air will take care of a lot more moisture, while the hot water will give you kitchen and bath hot water as well from 12 volts and can give you hot showers when out cruising.
I have been thinking about a radiant heater solution using an electric water heater with a pump
to move water around pex tubing under the sole and in the cabinets to keep them warm and dry. Not sure if it would work or not.
The only thing I would leave on when away from the boat is the furnace/boiler as they have sophisticated safety systems. Perhaps an oil filled radiator on low as well, to keep things from freezing but only when really necessary. The vornado will heat the boat quickly.
As you can tell I have put a lot of thought into this as I plan to live aboard year round in the North East. You will have a lot more moisture but it will be a lot warmer than the North East.
Of course a very good solution is to start around August or September and just sail south! Once everyone starts speaking Spanish you are likely far enough south to stay warm for the whole winter! That is my plan, but I will be listening for the steel drums on my coast the Caribbean sounds good about now! then you can go back up in the summer, or just keep going!