The United States has a very large mutual fund market. There are literally hundreds of different fund families and thousands of individual funds available, and all of them are vying for your investment dollars. In fact, there are almost twice as many mutual funds as there are stocks traded on the NYSEARCA and NASDAQ combined.

Faced by this daunting array of options, investors need to find a way to separate the wheat from the chaff. One simple way to accomplish this is to focus on the biggest mutual fund companies. After all, mutual funds that serve their shareholders the best tend to attract more assets, so size seems like a reasonable proxy for success, or at least a reasonable starting point.

The process is easy: list all of the mutual funds for any given family; add up their combined total assets under management, or AUM; and see which companies investors have collectively poured in the most money. Since the relatively free market in the U.S. is supposed to reward success and punish failure, the biggest fund families ought to be the ones that have served investors the best over time.

Fund Families Vs. Fund Providers

A subtle, yet important, distinction must be determined before the list can be made, and that is the difference between mutual fund providers and mutual fund families. A mutual fund family is like a brand name umbrella. Most investors encounter mutual funds through their family names, such as the first words in titles including Vanguard International Growth Fund or the Franklin Templeton Total Return Bond Fund. If you organize the list by fund families, you are going to get the initial title to match for every mutual fund in a group.

The mutual fund provider is the larger financial institution that owns the fund family. For example, Wells Fargo, or the fund provider, owns the Wells Fargo Advantage Funds, or the fund family. The tricky issue with fund providers is they often handle more than just mutual funds, and they may have more than one fund family brand out in the market.

For a variety of reasons, it is advantageous to focus on fund families instead of fund providers. For one, it is easier. This decision has a significant effect on total rankings; BlackRock, for example, owns the world's largest mutual fund family but falls somewhere between eighth and 13th in the fund provider category depending on what factors are included. BlackRock Funds top the list in terms of assets held by a single fund family, followed by other familiar names such as Vanguard, State Street Global Advisors, Fidelity Investments and Bank of New York Mellon - Dreyfus.

1) BlackRock Funds / iShares

The New York City-based BlackRock, Inc. released its first BlackRock mutual funds in 1998 in conjunction with PNC Financial Services Group in a deal struck because co-founder Larry Fink had an equity dispute with other members of the executive team and never looked back. The period between 1999 and 2009 saw enormous growth for BlackRock funds, which carry the title iShares instead of BlackRock, in part because the company uses an elaborate risk-management theory of fund management. This laser-like focus on risk serves shareholders particularly well during economic downturns. BlackRock was also one of the first companies, along with Vanguard, to really see the value in passive management, though there are certainly many impressive iShares funds with active management.

BlackRock was a leader in mortgage-backed securities (MBS) investments during the boom years of the housing bubble. Its iShares MBS Fund was released in 2007 with plenty of fanfare just months before the financial crisis started to unfold. Yet the iShares series was able to escape the crisis relatively unscathed thanks to a focus on ZIP code by ZIP code risk analysis. Other companies, which by and large just gobbled up securitized mortgages based on yield or market value, did not make it out as well as BlackRock.

Not only was BlackRock not bailed out by the U.S. government during the crisis, but the White House actually consulted it on how to keep the financial system functioning during the mid-crisis panic. Early estimates from 2015 show BlackRock's mutual funds manage more than $3.85 trillion in total assets; including exchange-traded funds (ETFs) and other products, BlackRock boasts more than $4.77 trillion in AUM.

2) Vanguard

If a random sampling of the population was polled about the name of the largest mutual fund company, The Vanguard Group would probably win in a landslide. Not only is it one of the clear winners in the modern low-cost investing environment, but no provider markets as aggressively or effectively as Vanguard.

Vanguard is the most serious challenger to the iShares series by BlackRock, with the two fund families accounting for well over 50% of all mutual fund-managed assets in the U.S. It is also Morningstar's most highly rated fund family, just ahead of American Funds , PIMCO and T.Rowe Price, and miles better than fifth place JPMorgan. The Vanguard Group is a little more conservative with its numbers than most providers, but the Vanguard mutual fund series managed an estimated $3.1 trillion in AUM as of January 2015.

3) State Street Global Advisors

The last of the big three fund families, defined as entering 2015 with at least $2 trillion in AUM, is Boston's own State Street Global Advisors, or SSGA. SSGA is the investment management wing of State Street Corporation and manages more than $2.45 trillion worth of assets.

State Street Global Advisors introduced the world's first ETF, the S&P 500 SPDR ETF, in 1993. The company caught fire shortly thereafter and became a major international player in the managed asset space. Nearly one-third of all SSGA assets arrive via non-U.S. investors.

The mid- to late-1990s were an incredible time for SSGA mutual funds. Excitement over its ETF products created a carry-over effect into the company's mutual fund offerings, and management took advantage of the dot-com fervor to more than quadruple total AUM in the five-year period between 1994 and 1999. By 2012, SSGA had put offices in 16 countries across five continents and employed more than 2,500 people.