Exchange-traded funds offer a convenient way to invest in sectors or niches that interest you. If you'd like to add some stocks with the biggest dividend yields to your portfolio but don't have the time or expertise to hand-pick a few, the Global X SuperDividend U.S. ETF (NYSEMKT:DIV) could save you a lot of trouble. Instead of trying to figure out which of the biggest dividend yields to grab, you can use this ETF to invest in lots of them simultaneously. It invests in 50 of the highest-yielding  U.S.-based stocks, weighted equally and capped by sector at 25%.

The basics
ETFs often sport lower expense ratios than their mutual fund cousins. This ETF, focused on the biggest dividend yields, sports a relatively low expense ratio -- an annual fee -- of 0.45% -- and it yields close to 6%. The fund is fairly small, too, so if you're thinking of buying, beware of possibly large spreads between its bid and ask prices. Consider using a limit order if you want to buy in.

This ETF is too young to have a meaningful enough track record to assess. As with most investments, of course, we can't expect outstanding performances in every quarter or year. Investors with conviction need to wait for their holdings to deliver.

Why seek the biggest dividend yields?
The power of dividend investing is often underappreciated. Healthy companies with the biggest dividend yields (or even more modest yields) can be powerful portfolio supporters, providing income even during market downturns. Consider parking them in an IRA, too, to postpone or avoid taxes on dividends.

More than a handful of companies with the biggest dividend yields had strong performances over the past year. PDL BioPharma (NASDAQ:PDLI) surged 45%. It collects royalties from lots of medications and yields 6.7%, but some worry about its dividend's sustainability, since many of the company's revenue streams will dry up in the coming years as patents expire. Bulls will point out, though, that PDL BioPharma has been adding new royalty steams to its mix, such as with a $240.5 million purchase of royalty streams from DepoMed that are mostly related to diabetes. In its third quarter, PDL BioPharma posted revenue up 14% over year-ago levels and earnings up 13%.

Energy Transfer Partners (NYSE:ETP) got its act together in 2013, upping its dividend slightly, but for the first time in years, and offering investors today a 6.8% yield. Its stock is up 26% over the past year, too. Energy Transfer Partners sports some 43,000 miles of natural gas gathering and transporting pipelines, as well as other assets it got via its acquisition of Sunoco last year. The master limited partnership, or MLP, has also inked a deal with BG Group for LNG exports slated to begin in 2019, and it has been shedding non-core operations. It has made a lot of strategic investments, but its debt levels have risen, too.

Other companies with the biggest dividend yields didn't do quite as well over the past year but could see their fortunes change in the coming years. Domestic tobacco titan Altria Group (NYSE:MO) yields 5.2%. It's facing challenges such as rising taxes, regulations, competition from discount cigarettes, a shrinking smoker base, and even counterfeit cigarettes. Still, Altria is dependable, with its latest quarter featuring revenue up 5% and earnings more than doubling. Bulls are hopeful about its move into electronic cigarettes (one analyst even sees them eclipsing regular cigarettes within a decade) -- but the FDA might regulate those, too. Altria releases its fourth-quarter results on Jan. 30.

Frontier Communications (NASDAQ:FTR) had a great 2013, rising 21%. The telecom company carries considerable debt but is still yielding a hefty 8.3%. Its stock has been heavily shorted, with bears worrying about its loss of landline customers and its debt. Not helping its debt situation is its recent decision to buy AT&T's wireline business and statewide fiber network in Connecticut for $2 billion in cash. Frontier Communications expects the deal to boost free cash flow in the near term, though, and it has been shifting its focus from landline operations toward higher-margin businesses such as broadband and serving business customers.

The big picture
If you're interested in adding some of biggest dividend yields to your portfolio, consider doing so with an ETF. A well-chosen ETF can grant you instant diversification across any industry or group of companies -- and make investing in and profiting from it that much easier.

Longtime Fool contributor Selena Maranjian, whom you can follow on Twitter, has no position in any stocks mentioned. The Motley Fool has no position in any of the stocks mentioned. Try any of our Foolish newsletter services free for 30 days. We Fools don't all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.