You can find many threads about choosing a Linux distribution if you search for it. A good site for your reference is
http://www.distrowatch.com
For BSD, I have used only FreeBSD before so I can't say much about it. But FreeBSD works well for me

I especially like to use fvwm2 as the window manager. It is highly customizable but just I still don't know how. What I know is the way to set up a wallpaper and that's all :P