Macs have better resale, are easier to use, make better (more efficient) use of the hardware, are more reliable, are more secure and their total cost of operation is lower than PCs.
PCs are cheaper, initially, than Macs. There are lot of people out there who know Windows so its easy to to find someone to comiserate with.
I have found noone with real experience in both platforms that prefers to use Windows for their desktop. Even if you're just going to use the machine for surfing the Internet, Windows and Internet Explorer are notorious for their security holes. The MacOS os layer (based on FreeBSD) is far far more securely written so it is harder to write viri for (and obviously, since Macs are a smaller part of the market, fewer people are writing viri for them to begin with).
In particular, once you understand generally how Macs do things, you can pick up new applications very easily. There is far more (needless) variation in how interfaces work across the Windows platform, so applications take longer to master.
The vast majority of large commercial software products out there have Mac versions, and its relatively easy to run either a virtual machine or "boot camp" (dual boot) if you must run Windows products on your Mac.
I have given members of my family Macs because I don't want to be their system administrator if I can help it. They can administer their own machines. If I had given them Windows, I basically would have been signing up for a no salaried system admin for as long as they had my gifts.
So what do I use for my desktop? I use Linux.
This is because I develop software, and I am fairly comfortable making configuration changes to my system. Although MacOS is based on FreeBSD and the basics of the OS are just as good for development, the overlaying GUI turns it into a very different system. The things that I know about Linux and UNIX sort of apply to MacOS - but they've made a lot of changes in the name of ease of use.
For developers, I'd say the best over-all platform is Linux. Its very easy to develop apps that run on all three platforms. However, it is difficult to develop Windows apps under MacOS, and painful to develop anything under Windows. And of course, nobody deliberately develops Linux apps under Windows and very few do it under MacOS.