A round of applause for my friend Rick Munarriz: He makes a strong case for Baidu (NASDAQ:BIDU) over Google (NASDAQ:GOOG) in this week's debate.

I'm not surprised. Rick and I both contribute to David Gardner's Motley Fool Rule Breakers newsletter service, and he long ago convinced me that the Chinese search king is a great business. But is it better than Google? I'll grant that it's easier for an $8 billion business to double. I'll also grant that Baidu buries not only Google, but also Sohu.com (NASDAQ:SOHU) and Yahoo! (NASDAQ:YHOO), in its home market of China.

But if you buy Baidu over Google on that basis, you're making a mistake.

Why you should love a sell-off
That's not an indictment of Baidu. I'm simply asking that you consider stock market history: Stocks falter, and once-dominant franchises fall away.

Here, Baidu is the faster grower, and deserves the higher multiple. Its growth is accelerating even as Google's growth slows. Skeptical investors have cashed in their shares of The Big G. "Of course Baidu is the better business!" the thinking goes -- how could it not be? It's growing faster!

Don't fall for that trap. We know all there is to know about Baidu's opportunity. We expect ever-increasing rates of growth, which we'll get for a while, but not forever. Can you imagine when the growth stops, when the sheen goes dull for the first time in company history? Investors will bail like a sailor in a punctured lifeboat.

Diversification isn't always diworsification
Google has already survived its deserters, and it's now positioned for more years of outrageous growth, thanks to cloud computing.

Google's cloud is arguably the world's largest, built upon what some say are 1 million servers operating worldwide. Capitalizing on that footprint won't be easy, with Amazon.com (NASDAQ:AMZN) and Microsoft (NASDAQ:MSFT) aiming for The Big G. But with Android, Gmail, Google Maps, Google Apps, and the Chrome browser, Google has managed a digital land grab like no other. All that "land" is ripe for advertising.

Baidu, not Google, is the one-hit wonder here.

But don't take my word for it. "It's about time for ad spending to recover, which is, of course, Google's primary source of revenue," wrote Motley Fool CAPS All-Star investor BSHumphreyII two weeks ago. "At the same time, Google seems to be diversifying and moving into some new businesses, which will be great in the long term."

Specialists are great -- right up until they can no longer afford to be specialists. Ask Sirius XM (NASDAQ:SIRI). Satellite radio was a wonderful, hypergrowth business right up until the moment that it wasn't. Could it be again? Of course, but at this point, its future hinges almost entirely on whether it gets adopted on the iPhone. For Baidu, everything hinges on China.

Buy these numbers
Finally, if you're going to use a relative growth valuation as Rick does, you need to know that Google, with a 1.08 PEG ratio, is priced roughly in line with the sort of growth that the Street expects. Baidu suffers from a 1.44 PEG.

The simplest way to think of this: Google trades for an 8% premium to its long-term growth rate, whereas Baidu commands a 44% premium. At worst, Google is priced at an appropriate discount, given its decelerating growth.

But that's at worst. It's more likely that analysts are underestimating Google now as much as they're overestimating Baidu. Don't say that you weren't warned.

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Baidu, Google, and Sohu.com are Rule Breakers recommendations. Microsoft is an Inside Value pick. Amazon is a Stock Advisor selection. Try any of our Foolish newsletter services free for 30 days.

Fool contributor Tim Beyers had stock and options positions in Google at the time of publication. Check out Tim's portfolio holdings and Foolish writings, or connect with him on Twitter as @milehighfool. The Motley Fool is also on Twitter as @TheMotleyFool. Its disclosure policy had to break out its googly eyed glasses for this rebuttal.