Mac is a religion. You really want to stay away from that.
Windows was good while it lasted. With Windows 8 it all goes the Mac way.
Linux is not an operating system, it's a kernel. The most popular operating system which uses Linux kernel... I think it's Android. After that goes GNU/Linux and probably FreeBSD. I'm not sure if you can install Android on PC but even if you can, it's really stupid idea. So you'd really want GNU/Linux. However, there is no "canon" version of it. As everyone's free to mix and match free software, there are many GNU/Linux distributions out there which are basically just different sets of the same components. So "going Linux" is not as easy as it sounds, however you have the freedom to try almost any distro gratis and then change it at your heart's content.
On the other hand there is a worrying trend of going touchscreen. Win8, KDE4, GNOME3 and Unity - all look like complete shit. With free software you can always choose a different shell, on proprietary - not so much.
For the computer newbie GNU/Linux is the best way to go. It's only weakness is lack of native games and music production software (or maybe I didn't search hard enough, but nothing matches VST yet).