A more cohesive experience across the desktop and applications, eg.:

- The look and feel is uniform. Admittedly somewhat less so, these days now that the Apple Human Interface Guidelines are largely ignored.

- Mac apps and generally more stable.

- Mac apps generally have more features.

- The Mac apps I use generally tend to tie into the hardware (hw acceleration, drivers, etc) much better. The benefit of controlling the vertical, I suppose.

- The keyboard shortcuts both exist and are the same across apps.

- The design patterns.

- The AppleScript/x-callback-url, etc).

- Third party apps generally tend to fit well into the above.

On Linux, almost everybody seems to have their own ideas on how an app should be arranged. With full desktop environments, like GNOME and KDE lessen this, but it's still really, really common.

That said, my money is still on Linux and other open source OSes, because I don't want a single company telling me what I can and can't do.