The right-click argument died a long time ago - those who don't have a remote idea of how to operate OSX will often allude to components of a Windows system in comparison to those of OSX. MacBook trackpad? Press with two fingers. Or use a USB mouse and, gasp, right click.
So far as efficiency or versatility, though, no OS has any particular in advantage, though Apple's pricing is notoriously high for their systems, which would affect a decision to replace machines in accordance to a fixed budget. In spite of this, OSX is a wonderful system to work with, and the excuse "MS Office is better used on a Windows system, obviously" is nonsense, as there's OpenOffice/Google's own line. Open-source/free alternatives FTW!
Security-wise, most Unix systems aren't the targets of too many variants of malware, as a large percentage of users simply accept the OEM machine's OS, which is often Windows in lieu of mass-marketing (Microsoft's clear advantage is the distribution of its OS's), though I myself opt for Unix systems as the infrastructure will not be affected by Windows-viruses (heheh, no C:/ drive so to speak), the target of less abuse.
No system is perfect, though.