It it is to be electric, I like the oil filled type that look like an old fashioned steam radiator. They are silent and create a column of heated air that rises to the ceiling, "mushrooms" and circulates down the walls. Then the air crawls along the floor back to the heater to be reheated and rise again. Plus you get radiated heat along with the convected heat.

It it is to be gas, the ones that are outside vented are safer than the unvented ones. Safer still are the ones that draw combustion air from outside and exhaust it externally too. The air inside is sealed off from the outside air. No unburned gas or exhaust fumes and get inside but you need to put a hole in the wall to vent it.

I know from my experiences with an unvented gas log that unvented heaters burn whatever is in the air over and over again. If there are any fumes in the air such as odors from painting, your nose and eyes will be irritated until you turn it off an open some windows.

There may be oil burners with sealed combustion but I don't know of any.