That depends. If you want a version with all of the latest changes, this does not exist (it is an ever changing code base).
There are release branches (versions of the code that were "frozen" for release, except for specific bug fixes and other specific patches). Using a dev release branch is somewhat stable (and features many recent changes). Using a beta release branch is pretty stable (and does not include many recent changes). Using a stable release branch is the most stable one (and does not include recent changes at all).
To find a revision used for any release, go to
omahaproxy.appspot.com and find it under "branch_commit", I believe.