I bought the SteamOS version. After doing some reading on the subject (and at the advice of a good friend), the SteamOS version has a bunch of plusses, and few minuses.
First and foremost being that without a Windows layer running on the device, framerates are 20% better on pretty much any game. Also, SteamOS is wayyyyyyy more small-screen friendly than Windows.
On the downside, SteamOS has less compatibility with games. But thus far, it hasn't really been a problem for me.