According to web measurement firm Hitwise, MySpace commands 73.82% of all social networking traffic. The data comes from Hitwise’s special social networking category, which tracks US traffic 57 leading social networks. MySpace took nearly 74% of all traffic to those sites in April, with Facebook second at 14.8% and MyYearBook third with 1.33%. Overall, social networking traffic is down 16% year-over-year.

Compared to April of 2007, MySpace has seen traffic decline 5%, while Facebook has seen a 32% bump. Even so, MySpace still controls the lion’s share of social network visits in the US. General social networking in the US is clearly a two horse race, and MySpace is ahead by a couple of furlongs.

Hitwise also noted that MySpace has seen an increase of 73% year-over-year in average time spent. So while they may be losing a small amount of total social networking traffic to Facebook, MySpace is better engaging the visitors it has retained. Interestingly, competing web metrics firm Compete paints a different picture, suggesting that year-over-year average stay has fallen 9.9%. Differences in how each stat is measured could explain the dissimilar results, however, though they are strikingly different.