Mac... PC...
Use whatever you are best fit with. I use Mac so I can test things in both OS X and Windows environments when I develope things. One thing is for sure.
Mac = Work, Graphics | Windows = Games

Of course both environments can be used for both things, but from personal experience games run better on Windows (if they are Windows only) and working is more fluid and safe in a Mac OS X.
I personally have an iMac 27" with a Windows Bootcamp when I wanna play some FFXIV.