Wi-Fi has come a long way since the days of 802.11b. It used to be the purist’s favorite sneering target, both for its sorely lacking speed and the fact that anyone operating a microwave within three miles would essentially render the 2.4GHz band unusable. Microwaves still throw out interference, but 5GHz means that’s not quite true anymore. That said, lower-end Wi-Fi does have its issues, particularly when there’s a lot of competing signal around. Finding a free channel in a built-up area can be tough, and fighting with metal and concrete structures is still a problem. Electromagnetic fields, too, are a big issue for Wi-Fi signals: If you’ve ever noticed a dip in signal quality over the holidays, you can probably blame those flashing festive lights.
Mesh, given its multiple points of contact, does help to alleviate many of the problems of Wi-Fi reliability. If one node is getting hammered, the second (if it’s in range) should be able to back it up—but if you’re relying on a wireless backhaul, your problem could simply be made worse. Ethernet? Once it’s wired in, it’s working—as long as nobody plugs in anything stupid. If stability is your concern, stick to the wires.