I’ve been a mac user since 1994, system 7, and it feels to me like the overall Mac user experience and reliability (stability, speed, etc) really peaked with Snow Leopard, 10.6.

This probably has a lot to do with the vastly improved hardware design around then - the touchpad specifically on the “blackbook” Core 2 Duo era macbooks was a step change, and they keyboard was pretty great too. Multi-monitor support was fantastic compared to everything else too.

You have to wonder what the design principles of pre-X MacOS paired with modern Apple hardware could achieve.