Kubuntu has fully matured and stabilized and comes with the brand new KDE Plasma workspaces and other KDE technologies. Like any other operating system Kubuntu also needs a little bit of work to get it ready for you. There are a few things which are optional and I have added them here based on my own usage, you may not need them.
Just about any Linux makes an excellent media server because it's lightweight and stable, so you can use whatever flavor you're most comfortable with. Any Ubuntu variant (Ubuntu, Xubuntu, Lubuntu, and so on) is exceptionally nice to set up as a media server because they make it easy to get restricted codecs. I have Xubuntu running on a ZaReason MediaBox. This is a simple system for playing movies and music. It is not a DVR (digital video recorder), and it doesn't need a TV tuner because I don't have any broadcast TV. No cable, satellite, nor over-the-air even. Don't want it and don't miss it. But if that's something you want you may have it, because Linux wants us to be happy.