The only thing surprising about the drop in Twitter's (NYSE:TWTR) stock price was how long it took to come back to some semblance of reality. After the steady ascent of its share price, up to $73.31 per share the day after Christmas, the real-world problems of monetizing its services and trying to turn around slowing user growth have brought Twitter's stock back down to earth.

But all is not lost for the company. Users may not be clambering to sign up for Twitter at the rate they once were, which is worrisome considering its early growth stage, but at least ad revenue is growing. That said -- and despite a rash of negativity over the past couple weeks -- Facebook (NASDAQ:FB) remains the king of social media. Facebook naysayers would love to point out a closing gap between it and the upstart Twitter, but it's just not happening, especially where it matters most to shareholders: ad results.

Some supporting data
According to research from e-commerce solution provider Shopify, Facebook isn't just the leader in social commerce -- purchases of products or services starting from the consumer's Facebook page -- the competition isn't even close. Last year, an estimated 85% of all purchases on Shopify-hosted online stores originated from Facebook. With over 90,000 e-commerce sites generating more than $3 billion in sales to date, there's certainly enough Shopify data to render the information statistically relevant.

The 85% of purchases made by Facebook users constitutes a 129% increase from 2012. Not only is Facebook leading the social commerce way, it's distancing itself from the pack. Twitter, YouTube, Pinterest, and a smattering of other social media outlets scrambled for the crumbs.

In terms of the amount spent by each social commerce consumer on Shopify's sites, Facebook was fourth, with an average spend of $55 for each transaction. That trailed etailer Polyver's $66.75 per order average and Instagram's $65. Customers originating from Twitter spent an average of $46.29 on each transaction, placing the Tweet-master seventh on Shopify's tally.

Remember Instagram, Facebook bears? That was the $1 billion acquisition from a couple years ago that Facebook CEO Mark Zuckerberg "overspent" on. Not many users, non-monetized, and few prospects going forward were just a few of the grumblings heard from Facebook analysts and naysayers at the time. Though Zuckerberg is vague in discussing Instagram specifics, rumor has it the service has doubled its number of users in the past year to 180 million, and it's clearly driving user advertising engagement.

So what?
Facebook was working toward diversifying its revenue streams, emphasizing gaming revenues as an example, even before its recent $2 billion deal to buy virtual reality leader Oculus. But Facebook's bread-and-butter, just as with Twitter, is advertising, and always will be. Last quarter was indicative of Facebook's operations: about 90% of its $2.59 billion in revenues came from advertising.

As noted in its recent earnings release, Twitter generated $243 million in Q4, up from a mere $112 million a year ago. Twitter execs announced revenue guidance of $230 million to $240 million this quarter. A little over 90% of Twitter's Q4 revenues, equal to $220 million, were ad-related, while the remaining $23 million were derived from "data licensing and other revenue."

Clearly, both Facebook and Twitter rely heavily on advertising, and that's not changing anytime soon. As a marketer with money to spend, one look at the results from the Shopify research makes the decision a simple one. Not only are more users going to e-commerce advertisers' sites from Facebook than from Twitter, they're spending more when they get there.

Final Foolish thoughts
Even accounting for its depressed stock price of late, based on the middle ground of 2014's revenue guidance of $1.15 billion to $2 billion Twitter is trading at about 18 times expected sales. Facebook? Based on analyst's average revenue expectations for 2014 of $11.37 billion, Facebook is valued at 13.8 times 2014 sales.

Recent acquisitions have raised concerns about Facebook, and its stock is just now clawing its way back from a sell-off as a result. But no matter how you measure the two, there's just no comparison between Facebook and Twitter, nor will that change in the near future. For investors interested in a social media play, Facebook remains the only alternative worth considering.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.