Snow Leopard was super stable. I can't remember a single crash.

10.6 was great for the time, I was actually really pissed after 10.7 and many releases afterward fucked up Expose during the Mission Control debacle (I think there's now a way to turn off the window grouping, but this was what ended up making me sell my 2012 MBP and switch to Fedora since GNOME 3 manages to have all the comfort features I liked from macOS).

and move away from the annual major release cycle again...