I use Linux because:
A) It's open source, and generally free. (With the exception of Red Hat and a few others)
B) It's generally more secure online, due to the fact that very few people have written viruses for it.
C) I like it better, it tends to be more stable than Windows, the only time it crashes is if you tinker around with it and
something up.
I don't use it exclusively though. Wine is good for running Windows software on Linux, but most games tend to have problems. So I run a dual boot system where I have Linux and Windows on the same harddrive, and switch between them depending on what I want to do.
And before you shout 'Linux freak!', I don't lnot like Windows, it's a good OS, it's just that I feel Linux is better.
My distribution:
Linux Mint