PC for sure!
Then again, it depends what you want to use the computer for, typically, if you are a student, a Mac might suit you for school use - but for anything aside school use - Windows will definitely be better.
If you're a Gamer - PC
If you're a Programmer - PC
If you're a writer - Depends, either.
If you're a student - Mac
Macs are more expensive, less powerful, incompatible, unreliable, misleadingly 'fast' (the truth is that Apple chips are slower than pentiums!), bulky with a 7GB OS, hardware customization will void the warranty, and you'll find yourself in Apple support more often than usual. :)
Well, thats just my opinion, as I have experience with both operating systems, I have to say - I loathe Mac, and Apple. Windows 7 is by far the best operating system money can buy.