Brightscope, which rates and ranks 401(k)s, released its third annual yearend rating of the 30 best large plans today. The Southwest Airlines pilots' plan took top honors this year, rising two spots compared with last year's list.

Brightscope's ranking system crunches more than 200 data points to simulate a 401(k) plan's effectiveness at getting plan participants to retirement, and its annual top 30 list serves as a cautionary reminder that all 401(k) plans are not created equal.

If you doubt it, look up your own plan (for free) at the company's website, which tracks nearly 50,000 plans and spans more than 30 million workers. There you will find a simple numerical score, based on analysis of the annual audit reports all plans file with federal regulators, and data provided by plan sponsors and record-keepers. You'll find tremendous variation in key success factors, including plan cost, employer generosity and the quality of investment choices.

This year's top 30 list underscores some positive trends in workplace retirement plans as companies rebuild from the crash of 2008-2009. The average Brightscope score among the top 30 increased three-quarters of a percentage point, and plan improvements made it more difficult to keep a spot on the list, says Mike Alfred, Brightscope's CEO and co-founder.

Seven plans are new to the list, mainly reflecting the rising competitiveness among large employers. The newcomers include Wellington Management Co., Deloitte , Bristol-Myers Squibb Co., BASF (BASFn.DE), Ernst & Young, Google (GOOG.O) and Vanguard. Meanwhile, IBM's 401k Plus Plan, which Brightscope singles out as a best-practices plan, slipped ten slots to number 22 - even though its overall rating only slipped to 84.7 from 86.2 a year earlier. "Their plan didn't really get worse," Alfred says. "The field is just getting much more competitive."

Brightscope's findings come in the wake of other reports indicating movement among plan sponsors to improve 401(k) plans. A recent survey by The Plan Sponsor Council of America PSCA.L found an unprecedented shakeup of plans, with just under 64 percent reporting that they had changed their investment line up in the past year.

The pace of change likely will accelerate over the next few years as plan participants receive and digest new quarterly statements that reveal more information on plan fees and investments. The new statements are mandated under U.S. Department of Labor rules that take effect next year aimed at improving transparency for participants and plan sponsors.

Fees already are falling among the largest plans, Brightscope reports. The 2011 top 30 had average total plan cost of 0.61 percent, five basis points lower than a year ago. By contrast, average total plan cost for all Brightscope-rated plans was 1.55 percent, and 0.87 percent for all plans with assets over $100 million.

The biggest single factor that won plans a spot on this year's top 30 list was funding levels - whether savings by participants or matching contributions. "Across all these plans, you see employees saving more than average and employers who are more generous than average," Alfred says.

That said, it should come as no surprise that a full 50 percent of the companies on this year's list are in the healthy energy and pharmaceutical industries; another 17 percent were financial services companies.

More broadly, employers are restoring matching contributions that were cut at the bottom of the economic crisis. The PSCA survey found that half of plans that suspended their matching contribution in the last four years have fully restored it; among all plans, 66.7 percent have maintained their matching contribution.

For Southwest's pilots, the number-one ranking means their plan "gets average plan participants to retirement faster than any other 401(k) plan in the country," says Bryan Lorenz, Brightscope's vice president of data. "A participation rate of nearly 100 percent as well as the highest combination of company generosity and salary deferrals contributed to this outcome."

That must explain why the airline's pilots have that legendary in-flight sense of humor.

The author is a Reuters columnist. The opinions expressed are his own. (Editing by Lauren Young and Beth Gladstone)

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