You'll never get a straight unbiased answer. Even people who own both almost always have a bias one way or the other.
I'm a web designer, and like the majority of web designers/developers I work on PC. I bought myself a mac a while back for cross platform testing, and I really wanted to fall in love with it, but it never happened.
There are a number of areas where it is possible to make comparisions between the pros/cons of each system here are my thoughts on a few things to consider:
Applications - As been pointed out already there is no difference between any major app running one either system.
Color accuracy - Some people will argue Macs are better for color accuracy, but if you really want you can buy yourself an Apple Cinema display (or better yet a Lacie or Eizo) monitor for your PC and use the Adobe calibration tools that come with CS. If I was principally a print designer I would probably be more tempted towards Mac, but I do print work on my PC (Lacie monitor) with great color accuracy.
Viruses - I have not had a virus for several years now, and in 10 years of running PCs have never had a virus that destroyed data. It's common sense - install decent virus detection software, update the virus definitions regularly, and don't visit dodgy websites. And don't open exectutable attachments in emails.
File extensions - One post in this thread suggests the fact that mac users often don't add file extensions to filenames is a reason to buy a mac. Ha! Most mac users (and applications) are now in the habit of adding file extensions - the lack of them is even frustrating to other mac users who may not have the same applicatin installed on their machine.
Cost - isn't such an issue as it used to be, as macs are priced more appgressively now. But PC still wins out.
Hardware quality - apple are renowned for the quality of their componentry. They are also known for their appalling after sales service when things go wrong. My studio mate, a print designer on Mac was without his new Mac for TWO MONTHS while the Apple dealer and Apple support argued about what was wrong with the machine and who should fix it. With a PC you have total control ovr the componentry that goes into your machine, and a LOT more choice, but with great power comes great responsibility
Perfomance - The fact that Apple switched to Intel processors should tell you something.
Gaming - If you plan on using your computer at home for gaming, then it's a no brainer which system is better.
Compatibility - What do your colleagues and peers use? Your life will be simpler if you are easily able to transfer files, network machines etc with the people around you.
*** appeal - Should be obvious who wins this fight. However with white now done to death, apple's new favourite color is black, which is the same color PC manufacturers have been using for years.
OS - It's like comparing Apples to oranges. No, wait, it's like comparing Apples to PCs! XP is looking very dated, but Vista is on the horizon and will *** up PCs big time. Again, there are fans of OSX, there are fans of XP, and never the twain shall meet... Just one thing: Don't believe peole who tell you Windows is crashy. This is not true since the advent of Windows NT/2000. I have run three XP machines over the course of five years, and have NEVER had a system crash.
Good luck making a decision! I'm sure whichever you choose you will love it.
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