I voted Linux, but my actual favourite is OpenBSD.
Iʼm amused by BSDs in general. Iʼd really like to switch (and I probably will). OpenBSD is especially good in my eyes for some reason.
Yet, I use Linux, specifically Fedora and CentOS.
On my desktop I use Fedora, with GNOME as my desktop environment. I use the fish shell, and a lot of fancy stuff. I even have a bunch of games installed that I use pretty irregularly.
On my servers I run CentOS (although we plan moving to CoreOS on some of them). Itʼs more stable, and has everything we need, most importantly security patches).