PC vs Mac vs Linux

Well, let's start with a background comparison of the three operating systems. 

1. Windows - Windows is one of the most well known operating systems developed by Microsoft. 9 out of 10 homes and businesses currently use at least one Windows computer. Windows was originally based off of MS-DOS. This line of Windows OS became known as the 9x series. Eventually, all subsequent Windows OS's are based off Windows NT. The most recent WINNT OS would be Windows 7. 
2. Mac OS X - OS X is an operating system developed by Apple and is currently the 2nd most used OS after Windows. It has less than 20% marketshare. OS X unlike Windows, is actually based off of Unix. Therefore, OS X is considered to be part of the Unix OS family like Linux is. In fact, you can almost consider OS X to be a Linux Distribution. 
3. Linux - Linux is not actually a single OS, but rather several distributions all based off of the original Unix system. Linux is very popular for servers but has recently found its way to the desktop. It's not as popular as OS X or Windows yet, but it's popularity is rising. Unlike OS X or Windows, Linux is free and open source. There are many distributions of Linux like Ubuntu, OpenSUSE, etc.

Now, if you watch TV, you might have seen some I'm a Mac commercials from Apple that criticize Windows. A lot of the information in those commercials is false. This next section is about common myths:

1. Viruses - In the Mac vs. PC commercials, it was stated that PC's commonly get viruses and Macs do not get viruses. That is untrue because OS X is just as vulnerable to viruses as Windows is. The reason why Windows appears to be more vulnerable is because it literally has more viruses programmed for it. But that doesn't mean the system itself is more vulnerable. Mac OS X has the appearance of no viruses because hackers don't think OS X is worth making viruses for. This is because barely anyone owns a Mac compared to the number of Windows users out there. Therefore, there's not much incentive to program a virus for a Mac. Mac viruses do exist and can affect a mac system just as much as a Windows virus can affect a windows system. There is no hacker proof or virus proof system. Even Linux systems have a few viruses. 
2. Stability - Many people say that OS X never crashes and is the most stable OS ever. The same can be said about Windows 7. Truth is, Windows XP-7 are the most stable operating systems ever. OS X can crash just as frequently as a Windows OS. In fact, OS X crashes even more when you are running non-Apple approved software such as Adobe Flash or Audacity. Even Steve Jobs admitted that Macs can crash a lot, despite what his I'm a Mac ads have said. The famous BSOD (Blue Screen of Death) on Windows is actually pretty rare now. It's a misconception from older Windows 9x systems (see above). Back during Windows 9x series, stability was actually an issue. However, the switch to Windows NT systems made the OS much more stable and Blue Screens are considered quite rare now. Apple and other Apple fanboys are using the Windows 9x history as an argument against Windows even though those systems have long been discontinued and those problems no longer affect modern Windows systems. As for Linux, it can crash too although it's much more rare than WIndows or OS X. When a Linux crashes, it's called a Kernel Panic.
3. Hardware - Normally in a Windows vs Linux comparison, I wouldn't mention hardware too much, but because Mac OS X locks users to Apple hardware, this comparison is necessary. For Windows and Linux, you can choose what you want to install your OS on. There's tons of options from manufacturers like Dell, HP, Acer, Gateway, Lenovo, Asus, and so on. For Mac OS X, you only have Apple. I'm going to use laptops as an example for this comparison because those seem to be very popular right now. Apple only gives you an Intel Core 2 Duo processor with 4 GB of RAM and a standard DVD drive on their MacBook Pros. That will cost you about $1,500. That same hardware on the Dell XPS running Windows Vista will only cost you about half of that today. Now, if you want more speed and power, then oh well, you can't on the Mac. Opening up a Mac will void your warranty and violate Apple's EULA. Now with a PC running Windows or Linux, you can have a Quad-Core CPU with over 16 GB RAM and a BluRay Drive all for the same price as a MacBook Pro. 
4. Software Library - Windows OS has the largest software library than any other OS. This means that the majority of programs, applications, and games out there are meant for Windows. Productivity Suites like Microsoft Office are always available on Windows first. That same version will be released on OS X later on. Many other programs out there are also Windows exclusive. If you're into gaming, you'll need good hardware (see above) and to play more games, you'll need Windows. Many PC games today are meant for PC's running Windows. There's a new line of games called Games For Windows, which is obviously meant for Windows. Many Steam games are also meant for Windows. Only a few games will work on Macs or Linux.
5. Usage - There's a common myth that Mac OS X is better and more common for video editing. This is untrue. Almost all video editing programs are multi-platform meaning they work on both Windows and OS X. Linux is an exception. Programs like Sony Vegas, Adobe Premiere, Autodesk Avid, and so on all work on both OS's. The only notable video editing program that is only for OS X would be Final Cut Pro. As for application and software development including game development, Windows is definitely the main platform. Many programs today are written in programming languages such as C++, C#, Java, and Visual Basic. While some of those languages work on OS X and Linux, the newer and more common ones are now for Windows only such as Visual Basic and C#. Game development for consoles and PC's are done primarily on a Windows platform for the same reason as above. As for server use, Linux is very common for use in large server systems and super computers. However, Windows is also common for server usage. It depends on preference and the amount of resources someone has. However Linux was originally designed with servers in mind. The server version of Windows, known as Windows Server is also Windows NT based. It's marketshare closely competes with that of Linux. OS X also has a server edition, however it is not very popular and is rarely used mainly because of cost issues. As I've discussed above, Apple software and hardware tend to be very expensive and overpriced. 

So which is the best OS? Well, that really depends what you want. I personally recommend Windows as it's the most well-rounded OS suitable for all your needs. Hope this information helps!