While both have there strong and weak points, Windows is ultimately the better OS, at least in my opinion. The higher amounts of compatible software really puts it ahead of OSX, as the latter usually requires a modified version of software already available for Windows that may come out much later. As many will tell you, Windows is supreme for gaming whereas OSX really lags in that department, which is a real shame.
While I'll gladly use both, I would, if given the choice, go for Windows.
Now, if we're talking hardware, then that is a completely different story.
If you ask me, Macs of most kinds are overpriced and underpowered. A Windows PC is not just one model of computer, but one you can build and install the OS on. Furthermore, you can still upgrade your machine and have Windows still running on it. And what happens if you try to upgrade a Mac with new hardware? It's bricked, you can no longer us OSX on that machine. At that point, you're better of installing Windows on it anyways. Now, going back to the power of Mac computers, they're essentially inferior hardware wrapped up in a shiny case with a large pricetag. And how does this sell? Because a lot of people don't know any better. Often, they're making the purchase because they're familiar with OSX and not so much with Windows, willing to play ridiculous amounts solely for the software while not knowing much or caring about the hardware.
Also, to anyone who brings up that "Macs can't get viruses" notion, just know that the reason that Macs seemingly don't have them is because many malware developers don't bother to create viruses specifically for Macs. Sure, you'll be less at risk if you use a Mac machine then a machine running on Windows, but preventing a virus from infecting a Windows PC isn't a hard feat, so long as the operator knows what they're doing.