Over the past two years, the market has experienced an incredible rally, especially considering how dire things seemed and how bearish analyst predictions seemed to be. But stocks pushed ahead, and over the past year, the S&P 500 saw a nice 13% gain. Even more impressive was the performance of emerging market stocks; indexes such as Vanguard's Emerging Market ETF (NYSE: VWO) saw gains of 17%.

However, the chatter about overheating in markets such as China and troubles in Europe have investors skittish about investing in international stocks. And rightfully so -- not every stock is going to skyrocket just because of country growth or extraordinary potential. You can get in trouble if you don't pay attention to macroeconomics and big headlines -- just ask shareholders of National Bank of Greece (NYSE: NBG) or Allied Irish Banks (NYSE: AIB), both stocks that took a beating in 2010. As the sovereign debt crisis continues to plague the EU, these are companies that you have to watch carefully as new developments can shift dynamics instantaneously.

That's why we've asked three of our top Fool contributors to scour the investing landscape and identify the worst stocks for 2011 (surprisingly, two of them agree on a single stock). I'd heed their advice and be extra careful before putting your hard-earned cash in one of these investments.

Alex Dumortier, CFA, Fool contributor
With cheap money pouring into emerging markets right now, they offer an embarrassment of candidates for 2011's worst international stock. The one I'm highlighting today is a good business with a price tag that makes it an unattractive stock.

MercadoLibre (Nasdaq: MELI), the eBay of Latin America, sports a hair-raising price-to-earnings multiple of 76.5 (based on normalized earnings-per-share for the trailing 12 months). The first time eBay (Nasdaq: EBAY) shares closed at a lower multiple was Feb. 2, 2005 (at 76.4). Since then, they've lost 24% of their value compared to a 27% gain for the Nasdaq index.

Admittedly, normalized net income at eBay has only grown by 6.5% (annualized) over the past five years. By contrast, analysts are forecasting annual earnings-per-share growth of 38% (!) for MercadoLibre over the next five years. Let's assume that actually pans out and that the shares gain 15.7% annually. In that scenario, the price-to-earnings multiple would end up at 31.6 -- eBay's current multiple.

That comparison suggests that the company needs to perform exceptionally well for investors to earn a 16% annual return -- the very minimum they should require to own the stock, in my opinion. My advice: Don't buy now when it comes to MercadoLibre.

Tim Hanson, advisor, Global Gains
I've been beating this drum for four months now, but I continue to believe that one of the worst international stocks to own in 2011 is MercadoLibre. Although many investors remain bullish on the "eBay of Latin America" (the stock is flirting with its all-time high), there are several troubling circumstances here that investors should note.

First, at 15 times sales and 40 times EBITDA, MercadoLibre is not only expensive, but I estimate that nearly 100% of the population living above the poverty line in Latin America would need to be online and regular users of MercadoLibre in order for the company to meet the expectations priced into the stock.

Second, revenue growth has been slowing recently and earnings inflated thanks to the recognition of unsustainable tax benefits. In fact, the company's effective tax rate in the most recent quarter was just 4.9%. That's low given that the corporate tax rate in Brazil, MercadoLibre's largest market, is 34%, and investors may soon have to come to terms with the fact that MercadoLibre isn't quite as profitable as they think it is.

Finally, although eBay is a significant investor in MercadoLibre, that company has opted thus far not to acquire its Latin American counterpart, but rather compete with it -- perhaps in the hopes of driving down the stock price so they can buy it at a cheaper price. This competition has the potential to put further pressure on MercadoLibre's margins by reducing the fees the company can charge sellers. While I remain optimistic about further economic growth in Latin America, I am skeptical that MercadoLibre can grow sales and profits at such a rate going forward to justify its current stock price.

Gerard Torres, Fool contributor
Bermuda-based Assured Guaranty (NYSE: AGO) will one day go the way of the woolly mammoth, or in financial parlance, the way of Lehman Brothers. Why? Because its services are no longer required.

Assured Guaranty is one of the only municipal bond insurers standing after the destruction of its competition during the financial crisis, but that won't be enough to save it. The business of insuring municipal bonds is quickly dying, as shown by the decreasing number of new municipal bond issues that have insurance. With only a little more than $18 billion in total assets, Assured Guaranty doesn't seem like much of an insurance policy compared to projections of a combined budget deficit of $140 billion for all 50 states in 2012.

If that wasn't enough, Assured Guaranty recently had its credit rating lowered because of expected losses from toxic mortgages, which is exactly what led to the obliteration of Assured's competitors. In other words, if you're a C student, then working with an A student will average you out to a B. There isn't much incentive to work with a B student, since you wouldn't get much of a bump. Well, Assured Guaranty, formerly an A student, just got demoted to a B student. So there won't be many suitors for its services in the future.

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Jordan DiPietro owns shares of National Bank of Greece. MercadoLibre is a Motley Fool Big Short short-sale selection. MercadoLibre is a Motley Fool Rule Breakers recommendation. eBay is a Motley Fool Stock Advisor selection. Motley Fool Alpha has opened a short position on MercadoLibre. Motley Fool Options has recommended a bull call spread position on eBay. The Fool owns shares of Vanguard Emerging Markets Stock ETF. 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.