When comparing SteamOS vs Debian Unstable, the Slant community recommends SteamOS for most people. In the question“What is the best Linux Distribution for gaming?” SteamOS is ranked 13th while Debian Unstable is ranked 24th. The most important reason people chose SteamOS is:
The OS natively supports Nvidia, Intel, and AMD graphics processors.
Specs
Ranked in these QuestionsQuestion Ranking
Pros
Pro Native graphics processor support
The OS natively supports Nvidia, Intel, and AMD graphics processors.
Pro Streaming service integration (under development)
Valve is in talks with streaming companies such as Spotify and Netflix to bring their features to SteamOS.
Pro For entertainment, it just works
What media center software do for videos, it does for games (and later videos).
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 Hard to install
If you've installed Arch you're probably fine, but for those used to simple installs like (Ubuntu to name just one) you should prepare some patience, determination, and painkillers. Good news is, it's getting better (it's very young).
Con Not built around the desktop experience
SteamOS is, first and foremost, meant to act as a gaming console - it doesn't ship with even some of the most basic applications, such as a file manager or image viewer. As a result, using SteamOS as your primary operating system would require a fair bit of work.
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.