They aren’t operating systems that I’d use today because of security and compatibility issues and because, let’s face it, they look old, but I loved some OS X releases because of their stability and performance. This were Mavericks and Sierra.
This two operating systems didn’t have new breakthrough features but they focused in performance and, in the case of Mavericks (10.9), the shift towards simplicity in the UI, leaving skeuomorphic design behind. On my old MacBook Pro, Lion was a disaster performance wise, and even tho Mountain Lion was better, it didn’t have that fresh feeling that I felt with Snow Leopard. Until Mavericks. Mavericks was pretty flawless and very stable, I really liked it.
The story repeated itself with Sierra. Yosemite was a burning garbage on my machine, and El Capitan was better, but not on the same level than previous releases. But with Sierra (10.12), the machine was again as smooth as with Mavericks. Then High Sierra came, and while it wasn’t a step backwards -and APFS was one of the biggest additions-, I never felt the system as smooth and responsive as with the above mentioned versions of macOS. And that was the last version my old MacBook Pro supported.
On my 2014 Mac mini Monterey is quite good, but when it comes to stability and performance on still supported versions of macOS, I would choose Big Sur. The last updates of Big Sur were quite good and the system felt pretty good performance wise.