A good diesel generator is going to need very little maintenance operating few hundred hours per year.
Why do people talk about engines like they are unreliable? They are modern marvels.
My Powerwall quietly sits there charged and waiting to be under load, and charges to full when storm mode is activated (or I activate it manually). It has a 10 year warranty, 15 years if part of a virtual power plant (which my storage participates in with the local utility). It requires no maintenance. I also received a 30% federal tax credit for the Powerwall, which the building will not receive for a generator.
TLDR Diesel generators where you might be without mains for a while and intend to replenish the fuel with deliveries during the outage, fossil gas for use cases where gas delivery pipelines are available (urban, suburban), propane for offgrid use cases (rural, cell towers, etc) where fuel longevity is a concern.
Generators need to be exercised and maintained. You are committing to fire that thing up for a few hours every month, just to make sure it's in running order when you need it (I used to work next to a hospital that fired them every week).
I had a 1990s car that started right up with 2015 fuel that sat in its tank for 9 months.
This can easily be automated, Generac will handle testing for residential generators.
Fuel is easy because we have an external tank with a visual gauge that you can read from several feet away. When they added DEF they neglected to add a DEF gauge that's as easy to read. Thank goodness they sell DEF at any old truck stop.
Do you really have a few hundred hours of power outage per year?
Around here, the power is so stable that we go multiple years without an outage that lasts longer than a few seconds.
If I installed a generator it wouldn’t a couple hundred hours per year. It wouldn’t run at all for years at a time unless I manually exercised it as yet another maintenance task for my already too long list of things to maintain.