This is oddly titled - because a Mac and a PC are essentially the same piece of hardware since Apple switched to Intel years back.
The question should be which OS do you 'prefer' - neither is 'better' than the other - and the way that it appears "Hardware" centric even though they run the same hardware.... right down to the CPU's these days...
And via BootCamp + Fusion, or VMWare/VirtPC - you can run either OS on either platform. Assuming your PC hardware is made in the past 3-4 years.. So thats Windows on Mac or Mac on Windows.
I use a MacOSX VMWare image for doing the Mac things I have to do as well as testing stuff and doing integration work...
I also use a Linux VMWare Image
and the hardware 'natively' runs Windoze.
So with the one PC - I have everything, MacOSX, Windows and Linux ...
And better for 'what' ?
Desktop Publishing, Imaging, Playing the Latest Games, Infrastructure Systems, Servers (and of what).... ?