Vanguard Group manages $3 trillion of assets, so it should come as little surprise that the Malvern, Pa., behemoth is a big player in 401(k) plans. In fact, 31 of the firm's portfolios rank among the nation's 101 most popular funds in 401(k) plans. No other fund company comes close.

A little over one-third of the big Vanguard retirement-plan products are index funds, a concept with which the firm is synonymous. Also prominent on the list are Vanguard's target-date funds, a solid choice for investors who want a one-stop, no-fuss option. According to Vanguard, 88% of all the 401(k) plans it administers offer its Target Retirement funds as an investment option, and 66% of plan participants invest in one.

But Vanguard has many actively managed funds, and eight of them also appear on the list. Like all Vanguard funds, these eight carry extraordinarily low expense ratios, particularly for actively managed funds. Low fees aside, we wondered how good these funds really are, so we analyzed them, ranking each one "buy," "sell" or "hold." And for those funds that we rated hold or sell, we offer alternative suggestions.

Vanguard Wellington: BUY

Symbol: VWELX

Assets: $88 billion

Expense ratio: 0.26%

1-year return: 11.1%

5-year return: 11.7%

10-year return: 8.0%

If you're looking for a good balanced fund for your 401(k), you won't do better than this one. Wellington, which typically invests about 65% of its assets in stocks and 35% in bonds, is the oldest balanced fund in the country. (It's Vanguard's oldest actively managed fund, too.) John Keogh, who runs the bond side, has been with Wellington since December 2006; Edward Bousa has handled the stocks since December 2002. Both work for money manager Wellington Management in Boston. Since their pairing, the fund has returned an annualized 8.2%, beating the typical "moderate allocation" fund (Morningstar's designation for its category) by an average of 2.5 percentage points per year.

Wellington has also stood up well to Vanguard Balanced Index (VBINX), another popular 401(k) choice. Wellington's 8% annualized return over the past 10 years topped Balanced Index by an average of 0.7 percentage point per year. Wellington is closed to new investors, so if it's in your 401(k) plan, you have a leg up over other investors.

Vanguard Primecap: BUY

Symbol: VPMCX

Assets: $46 billion

Expense ratio: 0.44%

1-year return: 17.9%

5-year return: 17.4%

10-year return: 10.5%

Our eyes are green with envy if your 401(k) plan includes this actively managed growth fund run by Primecap Management. This fund is closed to new investors, but that rule doesn't apply if it is offered in your workplace retirement plan. Buy shares in Primecap, and hold them for the long term. Over the past decade, the fund returned 10.5% annualized, an average of 2.5 percentage points per year better than Standard & Poor's 500-stock index.

Managers Theo Kolokotrones, Joel Fried, Alfred Mordecai and M. Mohsin Ansari, whom we recently described as the best stock pickers you've never heard of, invest in large, growing companies that trade at discount prices. Their approach is often contrarian--they venture where others fear to tread--and they dig into a firm's business and financials to find a catalyst for growth that will drive the stock higher over the next three to five years. About 60% of the fund's assets are invested in two sectors: technology and health care. Two biotech stocks, Biogen Idec and Amgen, and a traditional drug company, Eli Lilly, are the top three holdings.

Vanguard Windsor II: SELL

Symbol: VWNFX

Assets: $48 billion

Expense ratio: 0.36%

1-year return: 13.4%

5-year return: 14.5%

10-year return: 7.2%

The knock on this fund begins with its motley crew of managers: 12 all told, from five money-management firms, including Vanguard's quantitative analysis team. Each firm runs a slice of the assets. The theory is that because each firm has a slightly different approach to picking undervalued large-company stocks--the fund's broad mission--the mix of managers will offer investors a smoother, more rewarding ride than a fund that was entrusted to one manager or investment firm.

The outcome so far is mixed. Over the past decade, Windsor II has been less volatile than other funds in its peer group--large-company value funds--and it returned an average of 0.6 percentage point more per year than the typical large value fund.

But Vanguard 500 Index (VFINX), which tracks Standard & Poor's 500-stock index and is another popular 401(k) fund, edged Windsor II by 0.6 percentage point per year over the past decade. And 500 was slightly less volatile, too.

Vanguard International Growth: HOLD

Symbol: VWIGX

Assets: $21 billion

Expense ratio: 0.47%

1-year return: 1.7%

5-year return: 9.0%

10-year return: 6.7%

Strike one: a slew of recent manager changes--one manager joined in 2003, one in late 2009, another came in mid 2013, and yet another arrived in 2014. Meanwhile, Virginie Maisonneuve, who had been with the fund since 2005, left in late 2013; and Greg Aldridge, who joined as manager in 2008, left last year. Strike two: As is the case with several other actively run Vanguard funds, management is split among several sub-advisers--in this case, three investment shops. But we're not convinced that bringing more firms, more managers and more investing strategies to bear on a fund is a winning formula.

So why do we rate this fund a hold and not a sell? Since the financial crisis, something about the fund's menagerie management team has been working. Since the start of 2009, International Growth has posted an annualized return of 12.7%, way ahead of the 9.9% annualized gain of Vanguard Total International Stock Index (VGTSX), the typical foreign stock fund alternative in most 401(k) plans administered by Vanguard. This fund is worth holding if you already own it. We're hoping the game of manager musical chairs has ended, for now. Otherwise, go with the international index fund.

Vanguard Explorer: HOLD

Symbol: VEXPX

Assets: $12 billion

Expense ratio: 0.51%

1-year return: 7.2%

5-year return: 17.7%

10-year return: 8.8%

This small-company fund is not a disaster, but neither is it something to write home about. If you have access to a small-company index fund, such as Vanguard Small Cap Index (NAESX), you may find it a better choice.

Explorer, run by managers from eight shops, including Vanguard's quant shop, tilts toward growing companies trading at a reasonable price. One new group has piqued our interest: Chad Meade and Brian Schaub, who run Meridian Growth, a terrific small-company growth fund. Before that, they had a strong run at two Janus funds with similar strategies: Triton and Venture. Meade and Schaub joined Explorer's ranks in mid 2014 and were entrusted with 4% of its assets, so it's too early to say what kind of impact the pair may have. And it's not all that much money.

But that brings us to another concern: With $12 billion in assets, Explorer is the second-largest actively managed small-company fund in the country. (T. Rowe Price New Horizons is the biggest, with $15 billion.) When a fund becomes too big, it becomes difficult for a manager to buy and sell securities without pushing their prices in the wrong direction--down when they sell, up when they buy.

Vanguard Windsor: SELL

Symbol: VWNDX

Assets: $18 billion

Expense ratio: 0.38%

1-year return: 13.0%

5-year return: 15.7%

10-year return: 7.1%

Don't confuse this fund with Windsor II. Though they both invest in bargain-priced, large-company stocks, the funds have different managers. Wellington Management, the fund's sole adviser from its inception in 1955 until 1999, still controls about 70% of the assets. That share is led by Wellington's James Mordy. John Paul Goetz and Richard Pzena, of Pzena Investment Management, a New York City money-management firm, run the remainder. This is a far cry from the army of 12 managers (from five firms) who run the show at Windsor II. That may go some way to explain why Windsor holds 136 stocks, a relatively trim number compared with the 262 stocks in Windsor II.

Like Windsor II, Windsor doesn't pass muster with us. Windsor has been more volatile than the S&P 500, more volatile than Windsor II and more volatile than the typical large-company fund over the past decade. Instead of investing in Windsor, put your money in Vanguard 500 Index or any other low-cost large-company index fund in your 401(k) plan.

Vanguard Morgan Growth: HOLD

Symbol: VMRGX

Assets: $11 billion

Expense ratio: 0.40%

1-year return: 13.8%

5-year return: 16.3%

10-year return: 8.6%

This fund invests in large, fast-growing firms that have competitive advantages, strong balance sheets and smart executives. Over the years, like other Vanguard funds that are actively managed, it has been carved up among different firms--in this case, five, including Vanguard's quant group. The fund outpaced other funds in its category in six of the past 10 calendar years. But over the long haul, it has slightly trailed Vanguard Growth Index (VIGRX), which returned 9.2% annualized over the past 10 years. Plus, the index fund, with annual fees of 0.24%, is cheaper than Morgan Growth.

Vanguard Wellesley Income: HOLD

Symbol: VWINX

Assets: $41 billion

Expense ratio: 0.25%

1-year return: 8.1%

5-year return: 9.6%

10-year return: 7.2%

Wellesley Income is essentially the mirror image of the fund we recommend, Vanguard Wellington. Both funds are run by Wellington Management in Boston. But while the Wellington fund generally has two-thirds of its assets in stocks and one-third in bonds, Wellesley keeps two-thirds in bonds and one-third in stocks. Not surprisingly, Wellesley has benefited from the spectacular bull market in bonds. With interest rates so low, however, odds are that they will trend higher over the long term, and that will hinder the returns of Wellesley's bond holdings. (Bond prices and interest rates move in the opposite direction.)

Wellesley is 44 years old, so it has seen a few managers come and go. Wellington Management's Michael Reckmeyer handles the stock side; John Keogh, the bond side. The pair have been working together as managers on the fund since 2008. Their record together: a sturdy 7.9% annualized, nearly double that of the typical conservative-allocation fund (the category to which Morningstar assigns it). The fund offers low volatility, modest fees (roughly 70% lower than its typical peer) and a 2.3% yield. But because of all those bonds in the portfolio, we suggest you tread carefully.

Nellie S. Huang is Senior Associate Editor at Kiplinger's Personal Finance magazine.