in large part, better is subjective.
OSX has an excellent virtual memory manager, yet its a resource hog. Ubuntu, uses less resources so its "better" but yet people prefer OSX over that.
Likewise with windows, there are many points that people argue on, which are subjective. Yet there are metrics that are not subjective but quantifiable.
Performance - you can measure which app handles applications, including multi-threading and memory utilization
Stability - how easy is it to crash or compromise the system.
Application installation/uninstall - How easy is it to add and remove applications
Device drivers - depth of drivers available, quality of the drivers and stability.
security - how easy/hard is it to compromise the system.
subjective metrics, are the theme, ui, interactions, altering the look and feel and behavior of the OS All of these leads to one's opinion on which OS provides best environment.
Personally, I think the Mac does for most of the non-subjective reasons.
Stability, application installation, memory utilization (even though its a hog) etc etc
