The following commentary comes from an independent investor or market observer as part of TheStreet's guest contributor program, which is separate from the company's news coverage.

NEW YORK ( ETF Expert) -- Scores of investment gurus live on momentum and relative strength. They may advocate investing solely in those assets that have put together streaks over four, eight and 12 weeks.

Other media darlings don't care what happens in a shorter period. They may run with a particular theme for decades. For instance, Jim Rogers likes commodities and the China growth story, despite the bumps that may occur along the path.

Sometimes, the hottest three-month winners are the same investments that fit a longer-term premise. For example, in 2009 as well as in parts of 2010, commodities and commodity-rich nations benefited from U.S. government decisions that weakened the U.S. dollar. Those that believe in the dollar's demise over the long-term profited in shorter-term periods as well as year-over-year periods.

Some longer-term themes fall on deaf ears. The notion of cheap P/Es and an aging baby boomer demographic didn't help healthcare-related stocks in 2009 or 2010; healthcare-related stocks severely underperformed in year-over-year periods as well as longer-term time frames.

Interestingly enough, health care has rocketed year to date . Pharma ETFs and Biotech ETFs even look pretty sharp over the last 12 weeks, showing tremendous relative strength.

Some of the more popular themes with corresponding ETFs have struggled in the recent three months. For instance, small-cap growth assets experienced a remarkable 12-month ride on the idea that the U.S. economy is recovering and can continue to grow on its own. With U.S. economic indicators from housing to unemployment to consumer sentiment worsening, however, small-cap growth has had its difficulties over a three-month time period.

Similarly, energy and materials stocks dominated the one-year timeline on the theme of increasing demand in the developing world. Yet they've had difficulty building momentum in the near term due to emerging market credit tightening and questions about demand out of austerity-struck Europe.

In contrast, the most recent victors have been the non-cyclical ETFs (e.g., staples, utilities, etc.) as well as Japan ETFs on a "bounce-back" from an earthquake-induced economic contraction. Moreover, if three-month momentum is to be recognized as an indication of what is likely to outperform in the near-term, one might stubbornly conclude that we are in the latter stages of the current bull market.

Of course, there's no reason to adhere to momentum or to long-term themes alone, as some of your best laid plans will be decimated. Manias from dot-com to alternative energy to nanotech have been losing propositions.

Indeed, one may lay the foundation for his/her portfolio on themes that resonate. For example, I have been emphasizing the key roles that Asian neighbors play in China's growth for years, advocating ETFs like iShares MSCI Malaysia ( EWM), iShares MSCI Singapore ( EWS) or iShares MSCI Thailand ( THD).

Yet I'm equally cognizant of shifts in momentum . For that reason, I will incorporate investments with momentum, particularly those producing income like SPDR Select Utilities ( XLU).

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Disclosure Statement: ETF Expert is a website that makes the world of ETFs easier to understand. Gary Gordon, Pacific Park Financial and/or its clients may hold positions in ETFs, mutual funds and investment assets mentioned. The commentary does not constitute individualized investment advice. The opinions offered are not personalized recommendations to buy, sell or hold securities. At times, issuers of exchange-traded products compensate Pacific Park Financial or its subsidiaries for advertising at the ETF Expert website. ETF Expert content is created independently of any advertising relationships. You may review additional ETF Expert at the site.