In 1972, Alan Turoff designed a word game called Boggle, in which players must find words in adjacent letters within a plastic grid of lettered dice. Little did Turoff know that 40 years later Boggle-inspired games would become one of the most contested battles in mobile gaming. We set out to compare two of the hottest contestants – Zynga’s longtime favorite Scramble With Friends and newcomer Ruzzle from Swedish gamemaker MAG Interactive, which has made a real splash in recent weeks.

Both apps are free (Scramble With Friends does have a paid version too) with some items available for in-app purchase, although as is typical for word games with broad appeal, the bulk of the monetization is based on advertising throughout the gameplay.

We compared the apps using two metrics – App Store ranking, usually a rough indicator of download volume, and daily market share (DAU) as measured by Onavo Insights, which reflects how many users are actually still playing the app, day in and day out. Both metrics were measured for iPhones in the US.

What did the data reveal?

Ruzzle, which was field tested across Scandinavia during 2012, came to the US by storm in December 2012. In terms of App Store ranking, it quickly overtook Scramble With Friends on December 10th and has stayed consistently high ever since.

The full story, however, is evident in the Daily Market Share analysis. Ever since January 12th there have been more daily players of Ruzzle than there are players of Scramble With Friends. Ruzzle’s explosive growth knocked out Zynga’s all-time favorite and by late January had almost twice the DAU of Scramble With Friends. Was Ruzzle destined to be another long-time blockbuster? Maybe not…

In the first week of February, Ruzzle peaked. Since then, its DAU has been dropping consistently. This is a cycle that is repeated frequently in casual gaming and more so in those games with a social element: traction amongst early adopters, followed by explosive growth (that phase when all your friends seem to be playing the same game), and at some point, attrition kicks in and players start moving on. The social element means that this attrition goes viral as players find their friends are no longer competing against them and lose interest.

We all remember Draw Something, a fad which swept millions and seemed unstoppable, but then peaked, incredibly right when Zynga acquired the developer, OMGPOP. So is Draw Something dead? It is certainly far from the popularity it enjoyed during its hey day, but it continues to be a reasonably strong performer (achieving an Onavo AppRank of 78 in January). Very few apps have been able to sustain massive growth for extended periods of time and once the novelty wears off they converge into a smaller, stable steady state. Interestingly, the strongest long term player is Scramble’s big brother Words With Friends, an almost unbeatable blockbuster that reigns as the game with the broadest audience (January being an exception where it was dethroned by the freshly launched Temple Run 2).

We’ll continue to keep an eye on Ruzzle, Zynga’s With Friends titles and any other surprising entrants. You can keep track as well by following Onavo Insights’ top games index, which will continue to be updated on a monthly basis.