I'm curious how ole Bliz is doing. Last I heard, and its been a while since I checked, WoW had a world pop subscription of over 15 million. The most of any MMO ever at the time.
WoW is down to ~10million. Its not hard to have the most ever when, 1. most MMOs never top 500k, 2. those that did quickly cratered in subscription base.
As much as developers try there will NEVER be another MMO as successful as WOW.