At least by 'level value' on wow-census. http://www.warcraftrealms.com/census.php?serverid=24
Oddly enough, draenor is also the 14th largest realm in the US by character count.
I have watched wow census on and off for years now and I was kinda shocked by what I saw there today. I have no idea if any of this is factually correct since it all relies on how many people run the site's client.
If we are indeed the #1 guild when based on an algorithm combining character numbers, level, and activity, then we should not have any trouble being the first guild to be fully tricked out in the Cata guild-leveling scheme right?

