PC is the cheapest and the best. And if you really wanted to and knew how, you could run OS X on a PC outside of a virtual machine (I've managed to get as far as a kernal panic upon boot up but still, it ran).
PC does NOT equal Windows however (as PC stands for Personal Computer).
If you need something that works with everything then go with Windows (but look out for viruses). If you need something that's very stable, does not get viruses, is free, and works very will with what works on it but doesn't work with most of the things you're already used to, go with a Linux distro (Ubuntu is one of the most user friendly ones and is very stable). As for OS X, OS X is really only good for multimedia applications. However, OS X also does get viruses. Not as much as Windows, but it still gets them (as for Linux there are currently no known current viruses, and if there were, a security patch would be put out very quickly (within a week)). The thing about OS X, is that Apple updates all the software for it themselves (well, most of it; such as java) and because of this, security flaws in those programs don't get patched nearly as fast (which means after the flaw is known there's a lot of time for people to make viruses for it, before a patch is out or even being worked on). For example, there was a patch for flash (I think) which was VERY important. Apple never updated it and now thousands of Mac's are part of a botnet due to the delay in patching (not sure if they've patched it yet).
Anyways; you're best going with Windows as it's compatible with everything, but if you're worried about viruses and want a very stable system you should go with Linux. If you're big on multimedia creation you should go with OS X (Windows can do multimedia but OS X is the best at it (or so I've heard)). There aren't many multimedia programs out there for Linux however.
If you get used to the OS X terminal or Linux terminal you can use most of the commands on either system (as they use many of the same commands (or so I've heard)).