Heat pump vs gas efficiency and comfort
It's illogical to compare the efficiencies of gas to heat pump systems because the way they produce heat is completely different. One directly burns fuel to produce heat, the other consumes energy only to move heat around. The source heat for heat pumps is essentially free. Thus calculating heat pump efficiencies will yield numbers well over 100%, something gas can never do.

In addition, if you really want to determine the root energy impact of each system, you need to consider the efficiencies involved in producing the energy and delivering it to your home. This will vary greatly by how each energy form is produced. Hydroelectric has a very different efficiency than coal fed power plants. Some utilities vary the source of power seasonally and through the years, so the root number is a moving target.

While it is true energy costs fluctuate, it still makes the most sense to compare your actual direct costs from using each system. While the actual cost of energy will vary significantly through the years, unless there is a major change in your area regarding sourcing each type of energy, the relative costs of each type should not vary nearly as much. When comparing costs, you must consider installation costs, maintenance costs, and eventual replacement costs. Comparing only direct operating costs can be very misleading.