Typography - Mac's support of typography is a result of years and years involvement with the pre-press industry. Type-styles rendered with a Mac just plain transfer better when submitted to a service bureau. You get what you saw. If you're into pre-press Mac is the clear winner here.
Video Subsystem - Windows open architecture and PCI bus allow a wide non-saturated video subsystem. Video cards are made which exceed 6 Gigaflops of geometric rendering. Mac, though PCI, has a severely bottle-necked video subsystem so if you're into advanced 3-D rendering, Windows is the clear winner here.
Postscript Support - Mac natively supports both postscipt and PDF formats making them the clear winning here. Again, if you're into pre-press, Mac makes a lot of sense.
Raw Speed - Windows PCs have a serious edge here. Where time is money, processor speed can be very important. Regardless of how hard Mac advertising attempts to claim that the slower clock speed Macs are really just as fast as a PC, it just ain't so and proven so by every bench test out there. If you have the "need for speed" in gaming, software development, 3D rendering and other applications, Windows is the clear winner here.
Color Matching - Apple is the only OS and hardware which supports Colorsync™, the industry standard for "what you see is what you get" color matching. If you want your advertising copy of an egg to come out of the press with the same yellow you saw on the screen, Mac is for you.