What's your go-to server distro?

I've been using Debian for quite a while for samba file servers, jabber servers and web servers. I've used Red Hat a couple of times. And I've also used Ubuntu on a few VPS machines.

I'm curious what you guys use. I'm looking to dig deeper into the server distros and try to get really good with one of them to give myself some more employment options and I'm wondering if there is a particular distro that is more widely used. I know Red Hat is big in enterprise, but I've been reading that Ubuntu really has taken the cloud hosting space.