Whenever the question of which social network dominates the landscape is raised, it seems as if the same two or three major players are the only sites that ever earn a mention. If you’re judging social networks based solely on the number of users each can claim, this makes perfect sense.

But, as impressive as the numbers may be, total users is not the only measure of success for a social network. While Facebook and Twitter may rule the roost when it comes to total users, a few surprising names pop up when you look at the equally important statistics relating to user engagement.

In layman’s terms, user engagement refers to how effective a site is at keeping users interested once they sign on. A quick scan of comScore reports from March of this year shows that, while they may be the best at attracting new users, sometimes the major players in the social networking game don’t always do a great job of keeping those users interested.

Average Minutes per Visit

Average Minutes per Visit is one of the purest measures of user engagement. A low AMpV number means users are showing up, poking around briefly, and then heading off to the next site that catches their interest. Obviously, a user signing off as quickly as they sign on is not something most sites hope for. The following chart reveals a bit of a surprise when it comes to Average Minutes per Visit. Facebook, the king of all things social networking, can only claim to be the third best in this area. Tumblr takes the top spot in this measure, with social discovery site Tagged taking home the silver in second place.

Screen Shot 2012 05 16 at 5.39.10 PM 520x287 Sure Facebook has 900 million users, but its engagement is smoked by these other sites

Household names like Linkedin, Twitter and MySpace fall way below, not even cracking the top ten.

Average Monthly Visits per Visitor

Average Monthly Visits per Visitor is an effective measure of how much loyalty a site garners from their users. The sites that rank high here don’t just excel at providing an experience that makes users want to return time and time again. Facebook is back on top here, but unlike other categories where they crush other social networks, the gap is narrower in this case.

Screen Shot 2012 05 16 at 5.39.58 PM 520x283 Sure Facebook has 900 million users, but its engagement is smoked by these other sites

At 36 monthly visits per visitor, Facebook is the only site that can claim a number that amounts to multiple visits per day. Tagged clocks in at 18 visits, a little better than every other day on average. Meet Me Media and Tumblr tie for 3rd at 11 and the rest fall off quickly from there.

Total Minutes

Another key engagement metric is total minutes. Facebook is the clear winner here, with Tumblr and new superstar Pinterest also racking up impressive numbers.

Screen Shot 2012 05 16 at 5.40.36 PM 520x363 Sure Facebook has 900 million users, but its engagement is smoked by these other sites

While it’s no surprise that a site that can claim over 500 million users would dominate the total minutes metric, things get a lot more interesting in the middle of the pack, where household names like Twitter and LinkedIn fare not much better than sites like MeetMe and Tagged.

While Facebook and Twitter continue to dominate the discussion about what social networking site can boast the most users, as the user engagement numbers show, a huge audience doesn’t always equate to a richer experience for the individual user.