Exchange-traded funds, or ETFs, especially high-yield ones, can be one of the best investment tools for income investors. That's because dividend ETFs not only offer the advantages of diversification but also make investing a bit easier, as you can hold a basket of stocks without having to monitor them constantly. In a low-rate, volatile environment like today's, such high-yield ETFs can prove particularly useful for income-hungry investors.

But with so many dividend ETFs to choose from, it's easy to get confused. Moreover, not all high-yield ETFs are safe. So to help you make sound investing decisions, our contributors have picked three high-yield ETFs that they believe could power up your portfolio: Vanguard High Dividend Yield ETF (NYSEMKT:VYM)iShares Core High Dividend ETF (NYSEMKT:HDV), and WisdomTree SmallCap Dividend Fund (NYSEMKT:DES). Read along to learn more.

Diversified exposure and low expenses

Keith Noonan (Vanguard High Dividend Yield ETF): The Vanguard High Dividend Yield ETF offers investors solid income generation and exposure to a wide range of leading American companies at very low cost. The fund tracks the FTSE High Dividend Yield Index, holds 415 dividend-paying stocks, and is mostly comprised of high-yield large-cap companies. It currently yields 2.9% -- which is roughly 50% higher than the average yield of the S&P 500 index.

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While VYM is one of the most diversified dividend-focused ETFs on the market, it's still largely comprised of blue chip companies, and its 10 largest holdings account for roughly a third of the fund's assets. The fund's top five holdings by weight are MicrosoftExxonMobilJohnson & Johnson, JPMorgan Chase, and Wells Fargo, and eight of its top 10 holdings are also components of the Dow Jones Industrial Average index. 

Accounting for dividend reinvestments, VYM's total return has been roughly in line with the S&P 500 index over the last five- and 10-year periods, and the fund has very low management fees. VYM's expense ratio comes in at just 0.08%, or $8 annually for every $10,000 invested, which Vanguard says is 93% lower than the average expense ratio of funds with similar holdings.  

With broad diversification and low expenses, the Vanguard High Dividend Yield ETF stands out as an advisable way for investors to quickly establish a position in income-generating stocks across a wide range of sectors. 

A treasure trove of blue chip dividend stocks 

Neha Chamaria (iShares Core High Dividend): iShares Core High Dividend ETF is among my favorite dividend ETFs for several reasons, including a solid basket of stocks and an incredibly low expense ratio. As its name suggests, this ETF focuses on high-yield stocks, tracking the Morningstar Dividend Yield Focus Index, which owns 75 top high-yield stocks of companies with an economic moat that can sustain and grow their dividends.

That means the iShares Core High Dividend ETF provides double-edged security: high yields and growing dividends. Also, the ETF's portfolio is as diversified as it can get. As of April 14, 2017, consumer staples stocks constituted 23.83% of its portfolio, while energy, healthcare, telecommunications, and information technology each made up between 12% and 16% of the portfolio. Among sectors, financials has the lowest exposure, which is actually a boon for investors during a rising interest-rate environment. Not surprisingly, this ETF holds some top-notch stocks, including ExxonMobil, AT&T, Johnson & Johnson, Procter & Gamble, and Philip Morris, among others.

Dividends from a portfolio chockablock with such blue chip names are expected to be good, and that's exactly how it has been, which is why total returns from the iShares Core High Dividend ETF since inception have been way higher than the S&P 500's.

HDV Total Return Price Chart

HDV Total Return Price data by YCharts.

The best part is that this ETF also has a rock-bottom expense ratio of 0.08%, making it one of the cheapest ETFs in the space. The low expense, combined with a dividend yield of 3.4%, makes this one of the best high-yield ETFs you can find today. 

A winning combination

Tim Brugger (WisdomTree SmallCap Dividend Fund): It should be noted that WisdomTree's small-cap dividend fund may not be ideal as a large portion of a portfolio, particularly for investors who are quite risk-averse. Small-cap stocks often result in short-term fluctuations, though they offer long-term growth potential.

That said, this ETF is not your ordinary small-cap investment. For starters, its focus is income, and it's done a great job generating strong yields from small-cap stocks. WisdomTree pays shareholders a 3.72% dividend yield and with its emphasis on small-ish stocks also offers appreciation upside.

The small-cap label shouldn't scare investors off, because a full 40% of the fund's portfolio consists of companies valued between $2 billion and $10 billion. Not huge by some standards, but not exactly mom-and-pop companies either. The balance of the portfolio are stocks valued under $2 billion.

What also makes WisdomTree SmallCap Dividend Fund intriguing, aside from its nearly 4% dividend, is its historical performance. A $10,000 investment made 10 years ago -- right about the time WisdomTree's ETF became available -- would be worth $23,817 today. The impressive ETF has also beaten the Russell 2000 index -- which is largely made up of small-cap stocks -- each of the last 12-month, three-year, five-year, and 10-year periods.

This year WisdomTree's small-cap dividend fund is up 31.4% compared to 21.31% for its index benchmark, the Russel 2000. Does it warrant a predominant position in a portfolio? Maybe not, but a strong dividend yield and growth potential are needed to take a portfolio to the next level, and this ETF fits the bill.

Teresa Kersten is an employee of LinkedIn and is a member of The Motley Fool’s board of directors. LinkedIn is owned by Microsoft. Keith Noonan has no position in any stocks mentioned. Neha Chamaria has no position in any stocks mentioned. Tim Brugger has no position in any stocks mentioned. The Motley Fool owns shares of and recommends Johnson & Johnson. The Motley Fool owns shares of ExxonMobil. The Motley Fool has a disclosure policy.