For more than a century, investors have looked to the blue-chip stocks of the Dow Jones Industrials (^DJI 0.44%) for safety and security. Even in turbulent economic times, the leaders that make up the 30 stocks in the Dow have largely stood the test of time and still offer promising prospects for the future.

But even among the Dow 30, some stocks show more leadership than others. For investors trying to decide which Dow stocks are truly the best, is it smart to stick with the most massive companies you can find, or can up-and-coming players give you better returns? Let's take a closer look at the Dow to identify the gargantuans in the average with a critical eye toward deciding whether they're the ones that deserve a spot in your portfolio.

The biggest of the big
When you look at the five stocks with the largest market capitalizations in the Dow, you find five captains of the global economy:

  • Oil giant ExxonMobil (XOM -2.72%) weighs in with the biggest market cap by far, at a whopping $401 billion.
  • Wal-Mart (WMT -0.28%) comes in a distant second, with the discount retail leader fetching $232 billion.
  • Software bellwether Microsoft (MSFT 2.52%) has a $227 billion market cap, placing it at No. 3 on the list.
  • Conglomerate General Electric (GE 0.04%) takes the fourth position at $217 billion.
  • Computer pioneer and diversified information technology company IBM (IBM -1.47%) rounds out the top five with a $215 billion market cap.

ExxonMobil has put up impressive stock performance over the past year, rising more than 20%. But more recently, the company's results have raised questions about the sustainability of its growth, as both revenue and income fell during the third quarter. In light of falling production levels, Exxon may have to go on another acquisition binge, similar to its move two years ago to buy XTO Energy. When you step back and look at Exxon's returns over the past five years, you'll find just 2% average gains, which clearly reflects the relative weakness in energy prices over that span. If the global economy doesn't cooperate with renewed growth, oil and natural gas prices could fall further, adding to Exxon's long-term troubles.

Wal-Mart, on the other hand, has seen consistent stock performance, up 25% in the past year and averaging 11% gains since 2007. After a long streak of falling same-store sales, Wal-Mart is back on the growth path. Moreover, with the economy on rocky ground once more, the retailer's discount model is perfectly positioned to recapture higher-end customers and boost sales, just as it did during the 2008 recession.

For Microsoft, hope for its Windows 8 operating system and Surface tablet has helped push its stock price higher by 13% over the past year. But longer-term, it hasn't shown an ability to compete effectively with more adept players in the mobile market, which could potentially leave it behind as PC sales continue to decline. That's why its stock has fallen at a 2% annual clip in the past five years, and why even value investors are dubious about its future potential.

GE is one of the biggest turnaround stories in the Dow. After plunging during the financial crisis because of its GE Capital division, GE has come roaring back, using its energy infrastructure division as the focal point of its growth story. Its stock is up 45% over the past year, but it's still well off its 2007 levels. Moreover, a downbeat forecast during its most recent quarter shows how dependent GE is on the overall health of the global economy, and until the picture grows clearer, it's hard to have complete confidence in the conglomerate.

Finally, IBM has provided consistent returns for shareholders for years, as it has reinvented itself from its original emphasis on hardware to provide higher-margin services as well. With its competitors having difficulties, IBM is in prime position to capitalize on their woes.

Simply the best?
Looking at the Dow's top five, you can't really conclude that the biggest stocks in the Dow are truly the best. With all the challenges that they face, all five will have to work hard to sustain their leadership positions, and if they fail, rivals are waiting in the wings to capitalize on potential missteps.