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.

Symbol: VWIGX

Assets: $21 billion

Expense ratio: 0.47%

1-year return: 1.7%

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.

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.

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.