Facebook beat out MySpace to become the most popular social networking site in January, according to Compete.com.

In Compete's Top 25 Social Networks Re-Rank, which ranks sites by number of total visits, Facebook was listed as having over a billion visits for the month. By comparison, MySpace had a mere 810 million visits, according to Compete. The positions represented a reversal of fortunes from a year ago, when MySpace was the most popular site and Facebook was number two.

As for the number of visitors on the two social networking sites, Compete claims that MySpace had 58.5 million uniques versus 68.5 million for Facebook. But users seem to be getting a lot more out of Facebook these days, based on two other metrics provided by Compete. Over the last 12 months Facebook has steadily grown in the number of visits per unique visitor and time spent on the site. MySpace has tailed off, especially in the latter metric. Compete's data charted a significant drop for MySpace last summer, when the average time spent the site fell from 20 to about 11 minutes.

Compete also released data for Twitter. The microblogging service has a long way to go to catch up to the two superstar social networking sites, with only 6 million unique visitors and 54 million total visits in January. However, Twitter apparently experienced a meteoric rise in popularity in the last year, shooting from 22nd to third place in Compete's latest list. Most tellingly, the average stay at Twitter now almost equals MySpace's.

As Compete blogger Andy Kazeniac points out, if this trend continues MySpace just might soon be in the rearview mirror of more sites than just Facebook.

Compete estimates U.S. Internet traffic for websites based on the daily Web usage reported by more than two million Compete community members.