It's going to depend on several factors. There is no one universal answer. It will depend on:
- the source of your electricity
- the rate of leakage of methane in your gas supply
- the relative efficiencies of the gas and electricity cookers under consideration
- the impact on your domestic heating / cooling energy consumption of the additional ventilation required when cooking with gas.
So it's not possible to give a specific answer, with regard to your three criteria. For the specifics of your own case, you'd need to look at lifecycle assessments (LCA) for each of the energy vectors. But let's look at some generalities:
When would electricity be better?
If your electricity supply is not preominantly coal, and you've got efficient electrical cooking (e.g. induction hob, microwave oven, well-insulated convection oven), then cooking with electricity is likely to be better.
It's also likely that your electricity supply will get cleaner over the next 10 years, i.e. within the lifetime of any cooking device that you buy now, so the balance may tip towards electric within the lifetime of a cooker bought today.
When would gas be better?
- you can source your gas as biogas or as renewably-synthetisised methane, or if your electricity supply is almost entirely coal- or oil- powered;
- and if the whole supply chain of your gas has very low leakage rates (so, no shale gas, no leaky pipes, no leaky cooker)
then cooking with gas is likely to be better.
When is it all bad?
If your electricity is mostly coal, and your gas supply is as leaky as many seem to be, then cooking is going to be quite carbon-intensive either way; that is, there will be high greenhouse gas emissions per unit of energy that actually gets delivered into cooking. In that case, the best option to take you closer to sustainability is find an energy provider who can supply you with cleaner electricity or gas.
On the positive side
Cooking tends to be a pretty small part of overall energy consumption (a tiny few percent), so the overall environmental impact from cooking is likely to be a very small part of your total impact.
Here#s a quick outline on some relevant efficiencies. The reciprocal of the overall efficiency is the multiplier for environmental damage: for example, an overall efficiency of 33% means that 1 unit of energy used directly for cooking does 3x the damage: An overall efficiency of 50% means 2x the damage. 25% means 4x the damage. etc.
- gas-powered electricity tends to be ~50% efficient
- coal-powered electricity tends to be ~35% - 40% efficient
- electricity distribution losses might be of the order of 5-10%
- gas-distribution leakage rates can be around 10%
- gas cookers can be ~40% efficient
- electric cookers can be ~70-90% efficient
Remember that methane has a global warming forcing of about 21-25, relative to CO2, at the 100-year time horizon, so methane leakages are significant contributors to climate damage.