Six 529 college savings plans have been ranked as the nation's top plans by Morningstar analysts in 2011, while another 15 plans have received above-average ratings.  On the other side of ledger, seven 529 college savings plans were judged as "below average.''  

The annual rankings were based on a study of 58 529 plans that together manage more than 95% of the nation's $133 billion 529 plan assets, according to Morningstar.

This is the eighth year that Morningstar has reviewed 529 plans, and the second year that Morningstar has provided Analyst Ratings on plans as well as quantitative Morningstar Ratings on the investment options contained within them.

Listed in alphabetical order and by state, the top plans are:

Alaska's T. Rowe Price College Savings Plan, managed by T. Rowe Price;

Maryland College Investment Plan, managed by T. Rowe Price;

Nevada's The Vanguard 529 Savings Plan, managed by Upromise;

Ohio's CollegeAdvantage 529 Savings Plan, managed by Ohio Tuition Trust Authority;

Utah Educational Savings Plan, managed by the agency of the same name; and

Virginia's CollegeAmerica, managed by American Funds.

Fifteen plans received above-average ratings, 30 received average ratings, and seven plans were rated below average.

"Overall, the 529 industry has grown more competitive and responsive to college-savers' needs over the past year," said Laura Pavlenko Lutton, editorial director for fund research at Morningstar and a lead author of the study. "Plans have lowered fees, offered better investment options, and expanded distribution choices. None of the plans we reviewed this year warranted a 'bottom' rating."

Listed alphabetically by state, the below average plans were:

Schwab 529 College Savings Plan KS Direct

NextGen College Investing Plan ME Advisor and Direct

Minnesota College Savings Plan MN Direct

TD Ameritrade 529 College Savings Plan NE Direct

Upromise College Fund 529 Plan NV Direct

CollegeBoundfund RI Advisor and Direct

Tomorrow's Scholar College Savings Plan WI Advisor

Morningstar indicated that Below Average 529 plans are unlikely to keep up with the industry average over the life of the investment and that plans that earn this rating typically have weaker investment-option lineups or fees that the investment is unlikely to overcome and outperform. The firm also said it may have concerns about the program manager's stewardship practices. 

Morningstar's mutual fund analysts consider five factors: the quality of the portfolio of investment options; the investment options' performance; the skill of the options' managers; the stewardship practices of the 529 plan's administration; and the costs associated with the plan. Analysts then assign ratings of "Top," "Above Average," "Average," "Below Average" and "Bottom." 529 plans receiving a "Top" rating incorporate the industry's best practices, including solid investment choices at a fair price, according to Morningstar.

Here's a summary of the study's findings:

529 plan assets increased by 12 percent over the previous 12 months through Sept. 30. That growth outpaced market returns for the period.

Conservative allocation options in 529 plans have gained the most in asset flows during the first nine months of 2011 among Morningstar's static-allocation categories.

The tax benefits of a 529 plan improve returns for investors relative to similar mutual funds, which can add up to significantly higher returns over the long term.

Virginia had the most 529 plan assets of any state, with more than $29 billion in its advisor-sold and direct-sold plans.

Open architecture plans-which include a variety of asset managers' funds in their offerings-did not have a consistent performance edge during the past year over closed architecture plans, which feature just a single firm's portfolio strategies.

The rankings report is available at global.morningstar.com.