Gas or geothermal energy - advantages / disadvantages?

I didn't ask about domestic hot water storage volume. Just the thought of standing without warm water when we have guests (and we have a large family and accordingly frequent overnight visitors) totally put me off.

I know that, we are generally four, but since my wife's parents work professionally for 3 years in Paris and before that 3 years in Washington (USA) and so visit us for 1-2 weeks at a time (in addition, usually the sister who also lives with her boyfriend with us), the house can sometimes be filled for a week with up to 8 permanent residents... but even then there have been no problems so far, probably thanks to the 55-degree set temperature and 270-liter storage volume (which was recommended for 4 people anyway).
What I also noticed when we built the house was that some usually expensive or well-known fittings like shower heads consume significantly less water due to smaller water streams and better spray patterns, so when showering you also waste less warm water... whether that actually makes a noticeable difference, I don't know.