Zynga remains one of the best-positioned businesses I've seen. But its edge may be eroding. Don Reisinger over at News.com did some digging, and found that The Sims Social from Electronic Arts (Nasdaq: ERTS) is catching on with Facebook users in Zynga-like fashion.

Launched two weeks ago, Sims Social already has more than 23 million active users, according to its Facebook page. While that's short of Zynga's Empires & Allies, which attracted some 40 million players in the weeks after its launch, it's still an impressive showing.

EA may also be making history. Its launch of Sims Social marks the first time a developer other than Zynga has so quickly captured the attention of Facebook players. Expect Activision Blizzard (Nasdaq: ATVI) and Take-Two Interactive (Nasdaq: TTWO) to draw some lessons from this.

Take-Two, in particular, has a small following and average rating for CivWorld. Surprised? I was. Sid Meier's Civilization series has been a popular board and PC game for decades. Facebook success seemed all but assured at launch. So far, that hasn't been the case.

In this sense, CivWorld is just like most Facebook games: played by a small but loyal handful, and otherwise ignored. EA knows the feeling, having endured this malaise with Madden NFL Superstars. That game has yet to cross the million-player threshold despite the franchise's popularity with console gamers.

The implication? Facebook success is neither formulaic nor guaranteed. Perhaps Zynga's moat is wider than any of us imagine? Weigh in using the comments box below. You can also keep tabs on the social gaming movement by adding these stocks to your watchlist: