Back in the day, there was a clear division between a Mac and a PC. The Mac leant heavily towards supporting the arts. There were great applications for graphic designers, publishers, and even musicians. But the Mac had very little support for business applications, or for the gamer.
PC/Windows on the other hand supported business applications and home users, specificially gamers, but had minimal support for the artistic side. Although, mostly due to Open Source, that side of things wasn't as bad as business support on the Mac.
These days the barriers have become even thinner. There are probably as many applications for graphic design, desktop publishing and support for the other arts on Windows as there is on a Mac. In some cases, there may be even more support on the PC platform since the Open Source movement appears to support PCs (Windows and Linux) more than Apple.
So the choice really doesn't matter. It comes down to two things.
1) Are you expected to produce data in a format for one platform or another? If you need to produce files in a Mac only format, you'll need to go Apple.
2) What do you prefer? Personally I prefer Windows to OSX, but that's what I've been using since the Windows 3.0 days. I have an Apple notebook, but I always drift back to Windows to do what I need to do.
So, you really ought to make an informed decision. Go to an Apple store and see if you can demo a graphics program on an OSX machine.
Better still see if you can find someone to lend you an Apple computer. Perhaps an old laptop they've had sitting around for a while.
Play with it and see if it is something you want to live with for the next few years.