What is the better choice for OH: Raspberry Pi Zero W or Orange Pi Zero 512

Ok, but that is a very common misconception.
eMMC and SD cards are equally unreliable. Read on here (a hard to stop myth, unfortunately).
That is why “has eMMC” should not be a criterion in HW selection: it just does not improve anything.

(on a sidenote: commonly available eMMC cards might be better than the average SD card and for sure they’re better than the cheapmost SD most people buy, but you can also get ‘Endurance’ SD cards which then are on par or better than average eMMC ones).

Sure there’s some differences in hardware in Raspis, Odroids and other but in terms of reliability they’re negligible in fact.

An IMHO severe mistake that people make is to be biased by personal experiences they made and to then extrapolate that.
Yeah once bitten twice shy. That’s human by all means but still results in bad advice in almost all cases. @MDAR I think you’re a little bitten there because you wrongly attribute SD card failures you encountered to Raspis only rather than to any SBC.

On another sidenote, only 20% of causes for interruption of services is hardware (40% are software and another 40% is human errors).

This is why most people focus on hardware way more than reasonable.
If you want as you say “that it works, consistently” then your focus should be on the operating system and it’s availability features as this addresses those 80% SW + ops.

And the IMHO worst mistake that can be made is if your fixation on or taken decision for a specific SBC hardware enforces to use a specific OS (or excludes any of them) which is what happens if you decide in favor of an Odroid.
That’s a critical error in the selection procedure because the outcome is then based on whatever a negligible difference in HW is in what makes up 20% of total availability only.

It should be the other way round: determine your (reliability) needs, choose your OS based on what it can do for you in that regard, then choose the hardware.
openHABian has lots of reliability features specific to deployment as a home automation server, see link above.