In a ring full of heavyweight contenders, you'd better keep your guard up.

The North American railroad industry sports a cast of well-trained athletes eager to gather market share and growth momentum at every opportunity. I have long-maintained that Canadian National Railway (NYSE: CNI) wears the championship belt when it comes to the group's most attractive investment vehicle, but a knock-out performance by some of its peers in the fourth quarter of 2010 may have brought the pack to within striking distance.

The hauler reported a 19% increase in comparable adjusted earnings for the quarter, leveraging a modest 12% improvement in revenue. By contrast, Union Pacific (NYSE: UNP) punched its way to 41% earnings growth. For the full year 2010, Canadian National grew earnings per share by a more respectable 30%, even while absorbing currency-related impacts of a weakening U.S. dollar. Smaller rival Canadian Pacific Railway (NYSE: CP), meanwhile, saw adjusted EPS surge by 54% in 2010.

Accustomed to dominating the group in terms of operating efficiency, Canadian National did retain its dominance with an operating ratio of 63.4%, but Fools may wish to note that this marked the first sequential upward spike we've seen in this metric since the first quarter of 2010. In the third quarter, the company posted an incredible mark of 60.7% for this critical indicator of core profitability. With CSX (NYSE: CSX) targeting a ratio in the upper 60s for 2011, the continent's more efficient haulers may be preparing to challenge Canadian National's peer-leading performance. Norfolk Southern (NYSE: NSC), meanwhile, has some ground to cover after posting a fourth-quarter ratio of 73.2%.

Looking forward to the remainder of 2011, Canadian National expects some tempering of North American economic growth from the substantial improvements observed in 2010. Nonetheless, the hauler sees at least a 10% increase in full-year EPS, even as free cash flow contracts 24% from the noteworthy C$1.12 billion achievement for 2010. The company intends to focus growth initiatives upon several areas that I consider particularly promising, including metallurgical coal, U.S. thermal coal, iron ore, and intermodal container freight.

While I still consider Canadian National an accomplished champion that's capable of defending its hard-earned title, I must give CSX a Foolish nod as a potential title contender. Both companies are pledging their devotion to shareholders through dividend increases and sizable share buybacks, and both share top marks with respect to operating efficiency. In a fight that may be to close to call, I call on my fellow Fools to help decide the winner.

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Fool contributor Christopher Barker can be found blogging actively and acting Foolishly within the CAPS community under the username TMFSinchiruna. He tweets. He owns no shares in the companies mentioned. Canadian National Railway is a Motley Fool Stock Advisor recommendation. 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.