Before you get all charged up for an epic show down followed by a 'fanboy' flame war, let me tell you, this post will not be that. In fact, when it comes to Mac (OSX ) or PC (Windows) I use both and have for quite some time. The reason I am posting this 'rant' is because I am often asked what I use and which I prefer, or which the person asking should purchase. The only 'right' choice is an informed one, so here goes.
First things first, the title of this post is wrong. MAC vs PC is all wrong, even though you know exactly what I am talking about. A 'MAC' is a 'PC' also known as a personal computer. It is simply the same thing as any other pc, except it is made by Apple. Since Apple's adoption of Intel parts, this is more true than ever. The distinction you are referring to is the operating system being used. OSX vs Windows. Now the reason why there is even a distinction is because OSX will not run on non-Apple hardware, at least not without hacking it or using some sneaking tools. Windows however will run on pretty much anything, including Macs.
Now that that is out of the way, lets begin our comparison. The first thing you need to assess, is, what are your needs. Do you need to use OSX? If you need to run Apple software, which will only run on OSX, you may as well give up reading now and go with the Mac. Unless you want to make yourself a Hackintosh (which will take some work but is do-able) that is.
If you are only using the computer for standard programs eg: web browsing, simple word processing and image tools lets continue. For this option you could use Window, OSX or any flavor of Linux.
Budget. Lets face it, money talks. If you're looking to compare any Mac, to any pc, you will find there is a large price discrepancy. Apple products cost much more then their equivalent specked non apple counter part. You can get almost any pc with the same or better specs at often half the price of the Apple. Does this mean something? Yes. Although the immediate assumption is that Apple is a rip off, there is some sense in the "You get what you pay for category". When it comes to purchasing a new computer, company's such as Acer or Gateway will attract a lot of customers with their rock bottom prices, however, by achieving these rock bottom prices, they typically are produced with flakier components which will fail much sooner than the more expensive ones, or not perform as reliably as they should. Keeping this in mind though, if a rock bottom computer is $400 and lasts you a year, you can buy between 3-4 new computers for the price of one Mac, and with that in mind also, this means you could buy a new computer each year, continually upgrading to the newer features. I personally would still go for a mid range Dell/Toshiba/Lenovo(IBM) computer. They're not rock-bottom prices, but they perform very well. Score one for PC.
Upgrade-ability - Between Mac an PCs, upgrading in almost all instances is much easier then upgrading or changing components on a Mac. Macs are built so they are not easy to tamper with. This is good as it keeps people from modifying their components and inadvertently breaking the machine, however it also means typically if you want to upgrade your Mac, you're almost stuck buying a new one. PCs on the other hand (while it be laptop or desktop) are very easy to swap parts on, and an upgrade can be cheap. Score one for PC.
Reliability - This is a tough one to rank as in all of my years (using both) I have never had an issue with either system which I couldn't resolve easily, but both have crashed on more than one occaision. Having said that, realistically Windows is susceptible to more virus's and more prone to problems, but why is this? The reason is simple. Numbers. Windows has a much larger user base than any other OS, and because of this, it is the target for more attacks. If you're going to write a virus to try to steal information, you're going to write it to target the most amount of people, and thus, Windows. The other reason is, Windows simply runs a lot more programs than OSX, and is used by many corporations. Also If you have kids, or worked on a computer used by kids, you will often find they have installed something they shouldn't have and that is the source of the problem. Apple applications are fewer in number, and the majority of their widely used programs have written Windows based counter parts which are written by reputable authors. So for now, Score one for MAC, however I don't know how this will change in the future as Apple's popularity and number increases. There are viruses for Mac, they're simply less common.
Usability - This is another tough one to rank, as both have their pros and cons and a number of similarities. For example:
Expose = Windows flip (windows key + tab)
Command tab = Alt tab (same application Switcher)
Stacks = Same as Start menu
Dock = Quick launch bar (or install a dock tool like RK Launcher )
Finder = Windows Search (admittedly both suck and its best to use alternatives like Quick Silver / Google Desktop)
Safari = Internet Explorer (admittedly both suck and its best to use alternatives like Firefox / Chrome)
But when it comes to core usage, I do have to admit I prefer Windows. Things you take for granted in Windows (like copying and pasting a file) is not so easy in OSX. Additionally Programs such as Skype, MSN Messenger, etc work much better in Windows. I have also fallen in love with the Aero Snap and program thumbnails feature (which can be given to Mac by using either Clinch or HyperDock ).
Since this comes down to software choice, and Windows can be run on a Mac, Score 1 for both.
Form Factor - This is tie. Mac has some beautiful looking hardware, but there are many PC manufactures who create just as nice equipment. It comes down to preference. Score 1 for both.
The Verdict - MAC : 3 | PC: 5
Again this is trying to be an unbiased comparison, but PC / Non-Apple hardware wins this round.