I can't comment on what Google might be doing in the future with RCS. Well, I can't comment but also don't know. I personally like hg.

But if I were to take a poll of the informed and opinionated engineers sitting around me, they would almost all likely take git over hg.

In any case, git is in actual widespread use _now_ at Google, for Android and Chrome, and other open source stuff (some of which was moved recently from code.google.com to github).