Another vote for Mac.

Now that you can run both operating systems and even at the same time using VMware or Parallels not to mention Sun's free virtual box, there is no reason to go for PC.

The OS is more stable and responsive and UI experience definitely better.

The only reason I ever boot up Windows is if I need to use a VB macro or run Visio or Project. Otherwise I prefer all the Mac apps. In fact if Apple implement a proper VB interpreter, their iWork suite is pretty good and much better than Office 2008 in terms of day to day ease of use.