So I've decided to format one of my hard drives that I barely ever use and install a free, open operating system on it alongside my Windows 7 install. I'm torn between what I want to install, so I'm going to let the StackOverflow community choose for me. Decide if I should install a Linux distro, a BSD distro, or something else, anything else. Back up your answer with a reason why, and I will choose whoever gives me the best reasons to install their respective OS. I am extremely tech-savy and can handle whatever you throw at me, so don't worry about anything being too technical.
And a friendly interface isn't important to me. I'm not afraid of starting at a black terminal window all day... not that I wouldn't enjoy a nice GUI either.