The best Mac OS version is the one that your Mac is eligible to upgrade to. In 2021 it is macOS Monterey. However, for users that need to run 32-bit apps on Mac, the best macOS is Mojave. Also, older Macs would benefit if upgraded at least to macOS Sierra for which Apple still releases security patches.
Is macOS Catalina better than Mojave?
Catalina VS Mojave | Compatibility. There's no big difference, really. So if your device runs on Mojave, it will run on Catalina as well.
Is macOS Catalina better?
Catalina, the latest version of macOS, offers beefed-up security, solid performance, the ability to use an iPad as a second screen, and many smaller enhancements. It also ends 32-bit app support, so check your apps before you upgrade.