I wouldn't base your decision on Atmos.
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EDIT: because Anson42 said it MUCH better than I did...
Just to be clear, Atmos itself isn't a gimmick but the producing of Atmos effects through psychoacoustics is a "gimmick" in my view. The science behind psychoacoustics is very real, but Atmos from 2 speakers is NOT Atmos from a multi-speaker speaker system, it is just an approximation.
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I am sure Apple does the best job of implementing it on two speakers, but the reality is, Atmos was designed to be used with at least 5 speakers (better 7) including two surrounds and with the surrounds having upward firing speaker components. Apple is doing amazing things with acoustics, but at some point two speakers are just two speakers. And Atmos even as Apple implements it, is not universal across applications. I say this even as I love my HomePods and have a stereo pair on my desk.
The other thing I would say, is that many people report that the use of HomePods (original) with Apple TV is not optimal for a variety of reasons including the Apple TV sometimes resorts back to the default of piping the sound to the TV and not the HomePods, especially it seems if your WiFi is marginal.
So I would research that to see if you can live with the limitations. I know Apple improves it with software updates.