PC and Mac is the SAME PLATFORM. These computers are both built on Intel-based components (same chipset, same CPU, same video card, same HDD, same RAM etc). Only an idiot can set off Mac against PC, because Mac is just one another PC brand like Lenovo, Dell, ASUS etc.
So the correct poll question is: "MAC OS X or Windows". So don't be a layman, educate yourself
As about the operating systems. Of course Windows only. Because there are no Mac OS X alternatives for the software I'm using daily to do my work.