The surge counter displays unique accounts, has no multiple or failed downloads. Also keep in mind that users can have more than one mobile device or duplicate accounts.
Gmail currently has about 425 million active users, so it becomes the most used email worldwide. This figure is lower than the number of accounts, since there are more accounts created that active users, many users create double counting both for work, entertainment, love, etc.
What if there is no doubt that Gmail for Android is the most popular mobile application.
Hotmail is trying to outdo Gmail but for now fails to reach it. Only in the 15th anniversary of the mail, we speak of July 2011 announced that Hotmail had 360 million active users worldwide, for now there is no new information on the number of active Hotmail accounts.