When comparing Gentoo Linux vs SteamOS, the Slant community recommends Gentoo Linux for most people. In the question“What are the best Linux distributions for desktops?” Gentoo Linux is ranked 15th while SteamOS is ranked 27th.
Specs
Question Ranking
Pros
Pro Full control of the software
Pro Portage's emerge is powerful
Pro Can be officially systemd-free
Gentoo's default init system is OpenRC. Gentoo also officially supports systemd-free Gnome and udev. Users are free to choose any init system they want.
Pro Great for anyone who is serious about learning the intricacies of Linux
It's useful for both beginners and professionals. For the installation, Gentoo offers various types, which are referred to as stages. Basically meaning how in depth you would want to go into the process of installation. For beginners it's useful to choose for a starting distro due to its various stages that can be very time consuming but beneficial as you learn the composition in general of Linux.
Pro Portability
There are many architectures available for Gentoo : i386, x86-64, PowerPC, PowerPC 64, sparc, DEC Alpha, ARM, MIPS, PA-RISC, S390, IA-64, sh, m68k.
Pro Documentation and community are second to none
Provides a whole handbook to refer to during setup and usage.
Pro A very large collection of software is available
There are more than 19.000 packages available in the official repository. And even more with overlays.
Pro Gentoo does not impose a standard look-and-feel
Pro Live USB
Pro Fully customizable
The usage of advanced features like USE flags makes it more customizable than any binary distribution.
Pro Can by optimized to any given CPU by using proper compile flags
Since everything is being built on your PC you can tune the code to make use of your CPU.
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).
Cons
Con Not beginner-friendly
You have to read a lot of instructions to start, even if you are familiar with Linux.
Con Customized package installation can take a long time and cause installation failures
The Gentoo package management system allows you to configure what compilation flags packages should support - i.e. specific processor flag support (SSE, SSE2, etc.), -O1, -O2, -O3 optimization, etc.
If you accept one of the default flags, Gentoo downloads binaries from the server. However, if you decide to optimise, it can and will download all source packages and start compiling allthe programs and libraries on your system. If your chosen flags don't work with a particular library, installation will fail.
Con Has no live images with graphical interface
Full installation is hand-made with a CLI (Command-Line Interface)
Con Since everything must be compiled it takes a lot longer to update
And if you have to update the kernel or some heavy software like Chromium it can takes hours if not more on weaker hardware.
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 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).