Windows 7. There's really no call for anything else. I have an Ubuntu VM for Java/C++ coding and a Windows XP VM for some cruddy old proprietary assembler I need to write code for. The VMs help me separate work from play.
Anything of importance strictly on Linux - openSUSE. I work with my computer and online, thus I love security, stability and efficiency in my working environment / Desktop. 12 years ago I made my choice FOR Linux and thus against troubles.