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This article was originally published on Sept. 13, 2015. It was updated on May 5, 2016.

A great way to build significant wealth over time is to carefully study individual stocks, identify and invest in the most promising ones at times when they're undervalued, and then hang on for many years, keeping up with their progress regularly. That's a tall order for most folks, though. Fortunately, another solid route to riches is long-term investing in top mutual funds, with talented fund managers doing the research and decision-making for us.

According to the Investment Company Institute (ICI), there were more than 9,500 mutual funds out there as of the end of 2015. Which are the "top mutual funds," then? Well, of course, "top mutual funds" can be interpreted in many ways. For the purposes of this article, I used Morningstar's fund screening tool to find top U.S. stock funds. For my criteria, I demanded managers with at least 10 years of tenure at the fund, a minimum initial purchase amount of no more than $3,000, no sales load, an expense ratio (annual fee) less than or equal to the category average, five- and 10-year returns greater than or equal to the category average, and a five-star rating from Morningstar. That won't guarantee stellar results, but it will certainly help us zero in on great contenders.

The screen I used helped me narrow down that huge field to about 52 domestic stock funds. From those, I selected a handful that stood out in one way or another and that offered exposure to small, medium, and large companies.

Top mutual funds
Without further ado, below are three top mutual funds to consider investing in now or soon, with the aim of holding through 2016 and beyond. I've broken up some key information about them into two tables.

Fund

Focus

5-Year Avg. Annual Return

Fidelity Contrafund (FCNTX -0.65%)

Large-Cap Growth

11%

Buffalo Discovery (BUFTX -0.55%)

Mid-Cap Growth

10.9%

Perkins Small-Cap Value (JSCVX -0.46%)

Small-Cap Value

6.9%

Data: Morningstar.com.

Fund Name

Expense Ratio

Minimum Initial Investment

Dividend Yield

Fidelity Contrafund

0.70%

$2,500

0.3%

Buffalo Discovery

1.01%

$2,500

N/A

Perkins Small-Cap Value

0.81%

$2,500

N/A

Data: Morningstar.com.

The five-year average annual returns above are all impressive, but don't put too much weight on them. You always want to compare a fund to a relevant benchmark, such as the S&P 500 for large-cap funds, and you want your given fund to outperform it -- otherwise it's often cheaper to just invest in the benchmark's index fund. Still, any fund can have an unusually strong or weak year that plumps up or depresses its average. If you're intrigued by any of the funds above, dig into them more, looking up their prospectuses, reading what their managers say, and reviewing their recent holdings.

Be sure to read up on any fund you're considering. Photo: Wikimedia Commons user Benjwong.

A closer look at each
The Fidelity Contrafund mutual fund has long been one of the biggest around, and it has performed surprisingly well despite that. It invests in both "growth" and "value" stocks -- though, ideally, one would seek both growth and a good price from any investment. It's also relatively focused, with its top 10 holdings recently making up about 32% of its portfolio value. The fact that its top two holdings were recently Facebook and Berkshire Hathaway helps explain why it offers such a low dividend yield, as neither company has a payout.

The Buffalo Discovery fund holds small-cap, mid-cap, and large-cap stocks, but it has more mid-caps than bigger or smaller companies. Its managers have explained that while they're seeking growing companies that are benefiting from innovative products or intellectual property, they're also looking to buy into such companies at a good price, such as when they're temporarily depressed or overlooked by others. It recently had more than 20% of its assets in each of these industries: technology, healthcare, and industrials.

The Perkins Small-Cap Value fund has been around since 1987, and sports a below-average expense ratio. Per its management, "This defensive small-cap value fund seeks to provide attractive returns over a full market cycle by mitigating losses in down markets while participating in up markets. The strategy focuses on high-quality companies with strong balance sheets and stable earnings trading at attractive valuations." The Perkins fund recently had most of its assets invested in the industrials, financial services, and consumer cyclical industries.

For some people, even choosing among top mutual funds can be difficult. If that's the case for you, you have an even simpler alternative: invest in low-cost, broad-market index funds. (You might do that anyway, devoting just a portion of your portfolio to managed mutual funds such as the ones above.) Three solid contenders are the SPDR S&P 500 ETF (SPY -0.21%), Vanguard Total Stock Market ETF (VTI -0.21%), and Vanguard Total World Stock ETF (VT -0.15%). Respectively, they will distribute your assets across 80% of the U.S. market, the entire U.S. market, or just about all of the world's stock market. It's smart to include international exposure in your portfolio, and the third ETF above will give you that for a low price.