2017 has been a tumultuous year, with plenty going on in the political and financial realms. Yet the stock market has done quite well, and index funds that track popular stock benchmarks have given their investors solid returns. In particular, among the most popular exchange-traded funds, iShares MSCI Emerging Markets (NYSEMKT:EEM), PowerShares QQQ (NASDAQ:QQQ), and iShares Core MSCI EAFE (NYSEMKT:IEFA) have delivered some of the best returns.

Index Fund

Assets Under Management

Expense Ratio

Year-to-Date Return

iShares MSCI Emerging Markets

$31.4 billion

0.69%

17.77%

PowerShares QQQ

$50.4 billion

0.20%

17.68%

iShares Core MSCI EAFE

$26.2 billion

0.08%

15.10%

Data source: Fund providers, ETFdb.com.

Riding the technology wave

Among U.S.-oriented index funds, the PowerShares QQQ leads the field with strong returns in the upper teens. The ETF tracks the Nasdaq 100 Index, which is composed of the 100 top nonfinancial companies that trade on the Nasdaq exchange. Although intermingling of stocks across the Nasdaq and New York Stock Exchanges over the past several years has made both indexes more diverse, the Nasdaq still has a preponderance of technology companies within its upper echelon. That makes the index particularly susceptible to tech-stock trends, and when technology is in the ascendancy -- as it has been so far in 2017 -- the Nasdaq does well.

The PowerShares QQQ does a good job of tracking the Nasdaq, with a relatively low 0.2% expense ratio taking only a minimal portion of the overall return of the index. With ample liquidity from plenty of trading volume every day, the PowerShares QQQ is an efficient way for you to tap into the profit potential of the Nasdaq and amplify your domestic stock exposure.

Mutual fund section of newspaper.

Image source: Getty Images.

Capturing the world

What's noteworthy, though, is that international markets have, in general, outpaced returns in the U.S. That's true both in other developed markets, where the MSCI EAFE index governs, and in emerging markets.

The two iShares funds represented here not only blanket the world between them, but also have different approaches toward their investing strategies and business models. The iShares Emerging Markets ETF tracks emerging-market stocks, and it's designed for use by institutional investors, with high trading volumes and ample liquidity. However, as you can see from the 0.69% expense ratio, the index fund is relatively costly compared to other ETFs.

It's true that investing in emerging markets involves more expense than buying and selling stocks in the U.S. and in other better-developed markets, but even so, the iShares offering isn't the most cost-effective solution. That's why it's noteworthy that the ETF has outpaced some of its lower-cost peers.

Meanwhile, the iShares Core MSCI EAFE ETF is an example of a lower-cost philosophy from iShares. The core series of ETFs are designed for longer-term investors, with less liquidity, but lower expenses. Investors have the opportunity to pay just 0.08% in annual expenses using the Core MSCI EAFE fund, and that compares quite favorably to the 0.33% expense ratio that its non-core iShares counterpart charges.

Overseas markets have done well so far in 2017. Improving economic conditions suggest that a long period of sluggishness might finally be coming to an end, and many investors have seen international stocks as being better bargains than the U.S. stock market, especially after eight years of bull-market conditions. That has pushed up international index funds across the board, but iShares stands out with superior performance compared to other large providers so far this year.

Find the right index funds for you

2017 has been kind to these three ETFs, and the trends that have supported their returns will likely continue further into the year. By understanding why these funds have done so well, you can get some insight into choosing ETFs that are likely to be the best in the future.

Dan Caplinger has no position in any stocks mentioned. The Motley Fool has the following options: short January 2018 $114 puts on PowerShares QQQ Trust Series 1 and long January 2018 $125 puts on PowerShares QQQ Trust Series 1. The Motley Fool has a disclosure policy.