We have had, for the last 4 years or so, wireless networks at all our school sites that have been based on Apple Airport Extreme access points. We started prior to that with the third generation, round units ("flying saucers"), which would occasionally cease to function on one side or other. The interesting but annoying thing about that was that when one went down, it would result in a cascade effect, wherein 30-40% of the remaining units on campus would also fail out, all requiring a restart of the AP's.
This was cured by replacing the Flying Saucers with the square format APX 802.11n ("Hot Plates") access points. We would have less than one drop out per year per site with these, and their range and client capacity were much better. Those were subsequently replaced by the current 802.11ac units, which we call the "Tower of Doom". None of these has ever stopped working, even once.
With any of the Apple access points, we have had no WiFi connectivity issues of any kind except that the units have trouble handling more than about 40 clients at once, and general outside bandwidth problems unrelated to the internal network connection. Stability with Mac OS's 10.4 and up was never an issue. At home, where I also use a Gen3 "Hot Plate", there are no WiFi problems using 10.6, 10.7 or higher, up to and including 10.10.4, even when streaming movies into two devices. The access points were configured to automatically switch between 5 and 2.4Ghz channels as needed.
HOWEVER....
Because of the need to have multiple WiFi SSID's and offer better central management, we have moved to a Ruckus enterprise grade access point, and we are having some issues with some of the Mac hardware. Not with stability when in use at all, but newer iMacs in particular will fail to re-establish the connection through the access point to the network. The WiFi signal and connection to the access point persists, but not the connection beyond the AP. We're not sure at this point where the problem lies at this point, but as I say, it sounds like something different than is being complained of here. Other than reconnection after an idle period, we have no complaints about the stability of the WiFi with any of our Macs.
If anyone has anything to offer on that matter, please do.
Thanks