If somebody could guarantee that your PC would never suffer from malware, spyware or viruses - and that antivirus software was unnecessary -- how much would that piece of mind and increased productivity be worth to you in cash? $100? $500 ? $1000?
Macs may be afflicted tomorrow but I am talking about the present -- right now. Secure.
You can argue price all you want. The most important thing is the operating system. I have a Apple Powerbook (the MBP predecessor) that is five years old. I have lived with three major upgrades to the OS and the computer is still humming along smoothly. No bugs, no crashes, no viruses. Ease of use. I am never tweaking the thing to get it to recognize a wireless signal, to burn CDs, to download images. I am never reinstalling software, dealing with a registry (what is that, anyway?) or other time consuming chores.