I use Windows (Professional, pirated), but I prefer Linux. Unfortunately, the computer with Linux had all its hard drives wiped apart from one partition, which was just storage. I installed Windows because it would be quicker to get it up and running (and downloading, yes, I am a criminal. Workers of the world...), and I could not be bothered to install Linux as well (I have two computers, the one which used to have Linux previously belonging to my dad).
Pirated is always cheaper, especially if you download it for free! Cost: one writable CD. Beat that! My family has not paid for Windows since Windows 98 (which we got free with a PC, so really, we have not paid for Windows since Windows 3.1.1 (For Workgroups))!