Depends. For servers, FreeBSD and OpenBSD hands down.
Desktops are two different systems--Windows and Ubuntu Linux. I need direct access to the hardware for development (CUDA) on both, so I can't VM. Windows is needed simply because Linux has always failed to provide me with the business apps I need to successfully work with the outside world. Not trying to start a flame war; it's just my experience.
Laptop is Windows, with Linux as a VirtualBox VM. Simply because I want to GSD.
Desktops are two different systems--Windows and Ubuntu Linux. I need direct access to the hardware for development (CUDA) on both, so I can't VM. Windows is needed simply because Linux has always failed to provide me with the business apps I need to successfully work with the outside world. Not trying to start a flame war; it's just my experience.
Laptop is Windows, with Linux as a VirtualBox VM. Simply because I want to GSD.