When comparing Ubuntu GamePack vs Debian Unstable, the Slant community recommends Debian Unstable for most people. In the question“What is the best Linux Distribution for gaming?” Debian Unstable is ranked 24th while Ubuntu GamePack is ranked 26th. The most important reason people chose Debian Unstable is:
It is great for your daily desktop Linux due it good balance of stability and recent packages - it is also recomended by the debian project as the distro you should choose for desktop systems.
Specs
Ranked in these QuestionsQuestion Ranking
Pros
Pro Guaranteed gaming compatibility
Has 6 thousand Linux and Windows games that are guaranteed to launch in Ubuntu GamePack.
Pro Great for Desktop use
It is great for your daily desktop Linux due it good balance of stability and recent packages - it is also recomended by the debian project as the distro you should choose for desktop systems.
Pro Up-to-date software
Cons
Con Development version
Debian Unstable is intended as a development release, and as such is much more likely to break.
Con Not for users new to Linux
You need to know how to maintain Debian Unstable or you can easily bork your system. There isn't very much information available on how to maintain Debian Unstable either. I was fortunate enough to be involved in a now defunct Linux distribution where a forum member put together a how-to on how to upgrade Debian Stable to Debian Unstalble, as well as a separate forum where users could post tips or ask questions about Debian Unstable. One source I would recommend is the Siduction forums.