Gas heating is quite efficient, but the pipelines must be in place. The FF location advantage is that it can be set up free-standing to serve an area without needing “feeds” of any kind.
So I imagine that what is most economic will vary depending on circumstances and existing infrastructure. Head-to-head, with both available at lowest rates, I don’t know which would be better. US gas prices are going to remain very low for a long time to come. The situation elsewhere is more complex, depending on legal, political, and physical constraints on fracking, etc.
