At the studio we use Debian because of the package list and management, for example alsa-oss (great fix for Flash audio on 64 bit, just install, no need to configure).

We are considering going to Ubuntu, since it can share the package list with Debian and because their release schedule is every 6 months which matches our needs. Also Ubuntu makes it easier to just a bit more standardized tools and plug-in for example Firefox and Thunderbird (instead of the Iceweasel and Icedove, I know I can install them on the side, but if I can reduce the amount of setup and configuration on the minor packages/tools the better :D ).