Currently I am using gentoo as my main OS. My geeky nature is well satisfied with it.
Of course it is not for new users looking just for a windows alternative but it is the best out there. Unlike others OS which spoon feed you with precompiled things here you have to build whole things from scratch. Of course there is emerge tool and portage( without those I don't know how life will be) which is the implementation of FreeBSD ports on it. Also it is one of the few OS which have their own embedded systems sections. So you can run them on non supported hardware.
Of course there is a FreeBSD section also.
After much hew and cry when every one thought that gentoo is going to be dead ( including myself) it survived and i return to use it again. But it has got many of derivatives which are newbie friendly like Sabayon. To use them you don't need any expertise on it.