Each week, I like to publish the past week's hottest ETFs to share some new trends and niche ETFs out there and give investors some new ideas. For this week, emerging markets were hot and an especially strong performer has been the Treasury 3X ETF Short play, of which the 2X I started a few months back and has been the easiest (at least most expected/predicted) double digit gain I've had this year.

PIN - Powershares India - Up 22% - With Indian exchanges rallying close to 20% in a single day following the election of a pro-business party, investors have been buying shares in jubilant fashion. While I don't recommend flat out shorting a trend like this, it's entirely plausible that with this mass one-day move, the sentiment has gotten ahead of the fundamentals and perhaps a more diversified approach is appropriate via a straight emerging markets ETF such as EEM.

EDC - Direxion 3X Emerging Markets - Up 18% - With the aforementioned India rally, other emerging markets have been hot all year as well. With the trend continuing, as emerging markets took it on the chin on the way down, conversely, during the recovery, they are rocketing back up at a much faster pace than US equities. ECD is up 10 times the S&P500 over the prior 3 month period at 146% vs. 14.7% for the S&P500. While leveraged upward moves sound great historically, beware the long term degradation of value that occurs with these daily resetting instruments, especially if the trend is not rapid and sustained as outlined in this 3X ETF Short/Long warning.

TMV - Direxion 3X Short 30 year Treasury - Up 16% - A few months back, this seemed like a sure thing; and it was - with investors actually taking a negative yield in shorter maturity notes and a below-inflation yield in longer duration Treasury instruments just to have a place to stash cash during the storm, it was evident that there had to be a selloff in Treasuries in the coming months. It wasn't a question of if, but rather, when and to what degree. The play is now unwinding and while investors may have missed the easy money, as long as the financial crisis continues to abate, I'd expect to see yields continue to increase, driving the Short Treasury play further into the green. (See full rationale and other ways to Short Treasuries).

RSX - Market Vectors Russia - Up 11% - Russia has also continued its ascent, up double digits for the week and 92% over the prior 3 month period. Viewed as on the verge of default several months back, with oil rebounding and the global economy recovering, markets have viewed Russia's near-collapse in equities as overdone and investors have been buying back in in force. The ruble has appreciated around 15% against the US dollar since January indicating the worst may be over from a devaluation standpoint. The peak trading value for RSX was close to 60 in 2008 so a double from here is at least plausible if the global economy gets back on its feet.

Disclosure: While the author does not hold any of the aforementioned ETFs specifically, there is a position in TBT, which is the 2X Short Treasury ETF. Additionally, Long Jan 40 USO Call, which is a bullish play on oil.

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