The exchange-traded fund (ETF) marketplace is active, competitive and ever-growing. It's also very top-heavy; the biggest firms dominate a very large portion of total investment assets under management (AUM). For example, the top three providers in the United States – Blackrock's iShares, State Street's SPDR and Vanguard – handle more than 80% of all ETF activity.

The global market isn't much more balanced. The top four firms account for more than three-quarters of the $2.7 billion in ETFs. The German-based Deutsche Bank's ETF wing, called Deutsche Asset & Wealth Management, is the fourth major player along with the big American three. Invesco's PowerShares ETF series is a distant fifth in global markets. All told, the top ten largest ETF providers consumer more than 85% of all ETF assets.

ETFs are still a relatively young instrument class. Each of the five largest firms bring competitive advantages to the table that make them successful.

BlackRock's iShares ETFs

While there isn't much separating Vanguard and State Street in terms of total AUM, both are battling for a distant second to BlackRock and the wildly successful iShares series.

BlackRock didn't originate iShares; the series was acquired during a takeover of Barclays Global Investors in 2009. Barclays actually launched iShares way back in 1996. By 2015, iShares included more than 500 funds and almost $650 billion in AUM.

Thanks in large part to the success of the iShares ETFs, BlackRock boasts more than $3.5 trillion in total investable assets – a figure larger than all but three countries and representing more than one-fifth of the size of the U.S. economy.

IShares is most renowned for building its ETFs around leading global indexes, such as Barclays Capital, the Dow Jones, Morningstar and Standard & Poor's. These funds average the highest average dividend yield of any provider.

Vanguard ETFs

By the beginning of the second quarter of 2015, Vanguard had passed State Street Advisors as the second-largest ETF provider in the world. Vanguard is probably the most unique and noteworthy ETF provider on this list, and it had the best 2014 of any company in this market.

Vanguard can thought of as the Walmart of investment companies, with its lowest-cost mantra. Even though Vanguard offers some managed ETFs, this company cuts its teeth on tiny expense ratios for passively managed funds. Its FTSE Emerging Markets ETF (VWO) is especially noteworthy for its size ($60+ billion in AUM) and enormous volume (nearly 19 million trailing three-month trades).

What makes Vanguard different is that it is owned by its own funds, meaning that its clients are also owners.

State Street Global Advisors' SPDR ETFs

Founded in 1792, State Street Global Advisors offers more than 100 ETFs. Most of these are referred to as SPDR funds. The SPDR S&P 500 ETF (SPY) is the oldest and largest such ETF, with nearly $125 billion in AUM. SPY is the most actively traded ETF in the world.

The SPDR series is a little different in that all funds are formulated as unit investment trusts. They tend to track larger-cap firms in developed countries.

Deutsche Bank AWM X-trackers ETFs

Deutsche Bank's X-trackers is by far the largest non-U.S. ETF provider. This series was launched in 2007 and met with immediate success, although there is threat of serious price competition from Vanguard in European markets.

This was the original series of ETFs to target the money markets, credit markets and currency markets in Europe. It lags behind in North America and Asia, however.

Invesco PowerShares ETFs

Invesco PowerShares is part of Invesco Ltd. and was launched in 2003. Though much smaller than the aforementioned series of ETFs, PowerShares is notable for its rules-based quantitative approach. The company calls this the Intellidex strategy, where stock are weighted for capital appreciation potential.

The PowerShares lineup is dominated by one fund: the PowerShares QQQ (QQQ). More than five times larger than any other Invesco ETF, QQQ is one of the most popular ETFs in the world.