Long before Facebook, Twitter, MySpace and even Friendster, online dating was the most prominent social experience changed by the Internet. Since the early '90s, this $1 billion business has transformed courtship.

Of singles over 18 years old, 43% have browsed online dating sites, equating to 40 million active U.S. accounts and nearly 600 million visits per month, according to Mashable.

Several publicly traded companies compete for online daters. But just like dates themselves, not all are worth your time or investment dollars.

The strongest stock also happens to be the biggest. IAC/InterActiveCorp (IACI) dominates the category with a 20% market share, according to Online Personals Watch. IAC mixes popular destinations like Match.com and Chemistry.com with niche sites for people in certain demographics or looking to meet people with particular characteristics.

Growth for IAC's dating business has come both organically and via acquisitions such as February's purchase of rival OKCupid. And, like priceline.com and Amazon.com, the stock has shown bullish technicals by eclipsing its internet-era high.

Significantly smaller but potentially more lucrative than IAC is Spark Networks (LOV), a pure-play online dating company which operates more narrowly focused networks such as ChristianMingle.com, SingleParentsMingle.com and JDate.com.

Last month, Spark Networks reported a 28% boost in year-over-year revenue and a 30% increase in paying subscribers. Insiders recently purchased nearly $1 million of the small-cap stock, which trades at a 500x P/E ratio. While that may seem like too much to pay for love, right now the market doesn't seem to care.

While the U.S. has over 40 million active online dating accounts, China has more than three times that amount. Jiayuan.com (DATE), China's largest online dating site, listed on the NASDAQ in May. Despite doubling the number of active paying accounts since 2010, the stock has cratered in the past month. Given what's been a difficult year for emerging market stocks and China, in particular, Jiayuan.com is one name I wouldn't court.

Finally, the most provocative site also happens to have the least provocative stock. FriendFinder Networks (FFN), which owns the Penthouse brand and runs a bevy of sites with a more explicit focus, claims over 484 million members worldwide and 180,000 new members each day.

Despite those statistics, income for FriendFinder has dropped 32% year-over-year, leading the company to recently announce a reorganization into 14 separate divisions. A bevy of lawsuits relating to its initial public offering hasn't helped either. With shares now trading ominously under $1, this is a trade you don't want ask out.