Windows is an operating system for those who need the absolute best software compatibility they can get. Windows has trouble running at times and it is has security wholes. Windows was designed to be played with and be customized to how you want it (lol staying with in copyright of course) to be for you.
Mac OSX is a very stable operating system that comes with most all of the software you need and is by far the easiest to use. I still can not get used to the fact everything is done for me though. If you are technically challenged, do not care for Windows, or if you love Apple products then the Apple Macintosh is for you. The big flaw with Apple is there is ABSOLUTELY NO DIY COMPUTER BUILDING. I do not care for the hardware you get stuck with and can not change. Hardware customization is very important for those actively upgrading.
Finally, there is Linux. Linux is the best running operating system you can get and is also the ultimate OS in customizing (if you have the know how). Linux has so many distributions to choose from such as Fedora Core, Red Hat Enterprise, Ubuntu (the most common from what I have seen), etc. Linux has been the choice operating system for many programmers due to the ease of customizing, low requirements, compatibility with most hardware, and most of the time the OS is free. Lol Linux is probably the only OS you can get for free only due to the fact that it has been in what I would think to be a never-ending "Beta." Linux is not very common due to the lack of it being less-user friendly for the technically challenged, however recent distributions have begun to solve that issue with Windows emulation and user-friendly GUI. Linux does not suffer from spyware and virus attacks due to Windows being the most pre-dominent OS on the market.
One note on Mac OSX. OSX has a core and kernel with Linux FreeBSD coding at the heart. That's right Mac users you use Linux. This version of FreeBSD is just tweaked with ALOT of eye candy and a very-user-friendly GUI. This makes it very secure for the most part. However, concern has been growing within advanced users as the popularity of Apple computers are increasing. Windows is attacked not only because Microsoft can't build a brick wall to stop a virus, but also because of the fact it is the most used OS. If Mac OSX becomes the dominant OS of the world, expect spyware and viruses to begin infiltrating your hard disks. In the mean time make the switch from using Safari to Firefox. You will save the headache of someone stealing your logins or even worse your financial info. Sorry Apple users but Safari sux just as much as Internet Explorer. Make the switch to Firefox.