My preference is for GAS heating.
Electricity based heaters can give nightmare bills for tenants.
Typically, the good old Vulcan wall furnace does a good job. Even better if you can situate it so you can use a rear register to heat out both sides. eg, Lounge/meals (front) during the day, then flick the lever later to heat the hallway (rear) to the bedrooms (and hence bedrooms).
I've lived in my rental house setup like this, with young kids, and it worked a treat. We left it split 60/40 to the front.
Heater (reconditioned - like new) cost around $800 including rear register + install.
Cheers
Simon.