It's been just three years since Facebook (NASDAQ:FB) went public, yet the company has already grown to over $250 billion in market cap. A little over a year following Facebook's public debut, smaller rival Twitter (NYSE:TWTR) would enjoy its own IPO, although it chose to list on the NYSE instead of the Nasdaq due to the many technical problems that Facebook experienced with its offering.

While the two platforms tend to borrow features from one another from time to time (i.e. they love to copy each other), only one has had considerably more success in growing as a business and mainstream social platform. In more ways than one, Facebook and Twitter have seen their performance paths diverge by quite a bit.

One of these is not like the other
For starters, let's just take a look at how the stocks' performance compares. Twitter shares jumped promptly after going public, but that post-IPO hype wore off rather quickly and the stock has been rather volatile ever since.

FB Chart

FB data by YCharts

Following a second quarter earnings release where management was brutally honest about the challenges that the company faces, shares have tapped fresh all-time lows of around $27. In fact, that's just about where the IPO priced at $26 per share, even though shares immediately opened at $45 on the secondary market. Facebook was effectively a complete opposite, with shares falling by roughly 50% in its first few public months, only to recover once the company showed it could truly build a solidly profitable mobile advertising business once it started trying.

Mainstream vs. niche
Even though both Facebook and Twitter are household names when it comes to social networking, only Facebook is actually used by the mainstream. Consider how each network's user growth has been in recent years.

Fb Twtr Maus

Source: SEC filings.

It's true that both companies are seeing user growth decelerate, but it's much more appropriate for Facebook's user growth to decelerate as its MAU base has become so large. It's not as if investors can expect Facebook to be posting 20% sequential MAU growth rates like it could back in 2009.

But Twitter's user growth has slowed to an anemic crawl, even though its MAU base is but a fifth of its larger rival's. Not including SMS fast followers, Twitter added just 2 million MAUs sequentially last quarter, compared to Facebook's nearly 50 million. User growth for both companies is now largely coming from abroad, where monetization is weaker than in the U.S. and Canada.

Opportunity in disguise?
There's a contrarian in all of us, which brings us to the inevitable question: Are Twitter shares offering a bargain value if it can put together a turnaround while Facebook shares are about to run out of steam as its valuation gets stretched? With Twitter's recent decline, Facebook is now trading at quite the relative premium.

Company

P/S (TTM)

Facebook

18.6

Twitter

10.5

Source: Reuters. TTM = trailing-12-months.

But the reality is that there are many reasons why Twitter is in its current predicament, and 10.5 times sales still isn't cheap. For example, the company is essentially a non-player in messaging, and it still doesn't know how to convince prospective new users to sign up and login regularly. Twitter needs to make its product more approachable if it ever hopes to reinvigorate user growth, and I'm not so sure that it can.

Meanwhile, Facebook has already reached critical mass and already has its eye on how social networking will evolve over the next decade. Hint: its answer rhymes with Innocuous Drift.

Evan Niu, CFA owns shares of Facebook. The Motley Fool recommends and owns shares of Facebook and Twitter. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.