Macs are less prone to viruses, though they certainly aren’t immune. There’s a long-running debate about whether the Mac system is more resistant to viruses, or if virus creators are simply more likely to target the large user base of PCs; in reality, both factors likely play a role. Either way, it’s likely you’ll face fewer security risks for the time being with a Mac-based office, particularly if many of your computers are connected to the Internet.
Most Mac users find their systems are more stable and less likely to freeze or need rebooting than with Windows. Across multiple users this can add up to a lot less wasted time and less strain on technical support staff.
You may find some or even most staff would prefer to use a Mac. As Macs become more common in home use, employees will become more comfortable with the idea of using them at work.