It depends entirely on your needs really, however unless your familiar with open source coding and well any computer related coding linux is out of the question.
Windows : Gaming, never try gaming on a mac it's terrible, trust me i've tried. The most compatible OS by far, if you can't get something for windows you can't get it for anything else. 90% of people use windows in the world, so even though macs are windows compatible, 90% of people still use windows. For high spec machines, vista is the best, a much better operating system than xp, if your machine can cope with it, if not xp, is your choice.
Mac: No real advantages over windows whatsoever, a nice easy to use interface, not prone to virus' at all, compared to linux millions of software to download, compared to windows barely anything to download, can't game to save it's life. You can dual boot it with windows xp/vista for your gaming needs etc, also it's video editing abilities lie at it's appeal, also it's other media capabilities, ironic though that it can't play games. 6% of computer uses use mac osx, 4% of which dual boot with windows.
Linux: Personally I don't know much about it, but I know enough to tell you, if you don't know anything about it stay away from it, as I believe it requires knowledge in computer code to use to it's full capabilities. Advantage - it's free.
Personally I use mac os x dual booted with vista, however neither OS is better than the other, I use OSX as my primary OS, but windows for my games and what not, there is also nothing Osx can do that vista can't, whilst there is plenty vista can do which OSX can.
Unless you have the money to invest in a mac and a copy of windows vista/xp, i'd stick with windows, 90% of people use it as their primary operating system, and another 4% of people have it. I also spect you'd find anyone who knows how to use a computer, knows how to use windows.
My suggestion - Windows is the way