Debian works well for me though I have tried a number of different distros. If Windows is ever needed, it's either on a dual system or can be installed inside VirtualBox.
Well, I am using Windows 7 for my entire office servers. But personally, I using Linux for my own PC. because I had a bad experience when using Windows. The main reason there is a virus. All this time I feel that linux is more secure from viruses than Windows