[Panzer04]

It doesn't really matter. You should insulate anyway to save energy, but a heat pump will still use 1/4 the energy as resistive electric for the same heat. Depends on your gas prices as to whether it's worth it, but it almost certainly would be.

A worked example - In AU gas is metered per MJ - 3.6MJ/kWh. So 3c/MJ means that gas is equivalent to electric heat at 12c/kWh. Heat pump multiplies that by roughly 4x, so 48c/kWh is the Breakeven point for a heat pump vs gas heating.

Heat is heat, it makes no difference. insulation would save you money on all heat sources though, and can be a pretty cheap upgrade (insulating the roof space, for example).