To me leopard is the most iconic. In my head it’s the wallpaper of modern macOS. I still remember back in the day that was the first thing I downloaded when I tried to make my Vista PC look at least a little bit like a Mac :-)
I remember being in awe as I set up that computer and that was the first computer I started writing some HTML on. All these years and 2 Macbooks later my career is in web dev and I _still_ love MacOS.