I'm using Fathom for my personal sites now and Plausible at work.
I did this 1) because of EU privacy rulings and 2) because Google Analytics is deprecating GA3 (which is website focused) for GA4 (which is app focused). The UX for GA4 SUCKS. It is so hard to find basic info like what pages are people most looking at, a realtime view, what are all the domains referring people to me, etc.
So far I like plausible better, it's simple and focused on websites. Whereas fathom seems ready to hook into more complex martech that I have no interest in.
That said, Plausible supports Google Analytics already and Fathom doesn't yet. In contrast, Plausible doesn't support TFA and Fathom does.
Plausible also has alerts on spikes and sends summary emails at your desired frequency whereas Fathom doesn't seem to do either.
So I guess the analytics market is still somehow in early days.
Also, Michael Lynch pointed out to me that if you plan to sell a site, buyers expect access to Google Analytics data specifically. Something to keep in mind.
Also, it's good to have server side analytics since this will uncover at least 100% more legitimate users (on tech sites especially). So I tried out Fastly and Netlify which show basic analytics but don't give you access to access logs. I ended up just hosting on an OVH VM with 7day block-device backups in case it goes sideways.