The best online game is a debatable subject, but statistics show that the most popular is World of Warcraft, which had more than 7 million active subscribers as of March 2015.
After its release in 2004, World of Warcraft saw large increases in subscribers. It reached its player peak in 2010 with over 12 million active accounts but has been steadily dropping since then. Even with that decline, World of Warcraft still claims to be the No. 1 online game of all time.
As of 2015, World of Warcraft features five expansions' worth of content and hundreds of hours of gameplay.