Dividend investors face a constant battle of choosing between dividend yield and sustainability.

Generally speaking, low yields are often sustainable but may be undesirable for investors looking to pad their portfolio with dividend income or reinvestment opportunities.

On the other end of the spectrum, high yields (let's say 5% and higher) are extremely attractive for income-seeking investors, but they're also often far more dangerous than lower yields due to a possible lack of sustainability. Remember that dividend yields are a function of payout divided by share price, and if a stock's share price has been tumbling, its yield will rise. Thus, dividend investors have to be diligent to ensure that a yield isn't inflated solely because a company's business model is in trouble.

Three dividend stocks yielding at least 11% you should consider buying

Here's the good news: Not all high-yield stocks need caution tape wrapped around them. After perusing just over 100 of the highest-yielding stocks, I've come to the conclusion that the following three, which just happen to be yielding in excess of 11%, are relatively safe bets that income investors may want to consider for their portfolios. And at over 11%, you could double your money, with reinvestment, in less than seven years!

Annaly Capital Management: 11.2% dividend yield

There are few industries more synonymous with high-yielding dividends since the Great Recession than mortgage real estate investment trusts, or mREITs. Arguably, the leader of the pack is Annaly Capital Management (NYSE:NLY).

Image source: Flickr user Mark Moz.

In really simple terms, mREITs like Annaly Capital do their best in falling interest rate environments or persistently low lending rate environments. This is because they earn money based on the difference of the rate at which they borrow and the rate at which they lend. As rates rise, this difference, known as net interest margin, tightens. Companies like Annaly Capital Management use leverage to compound their profits, but have a hard time levering up during an environment when lending rates are rapidly climbing. With the Federal Reserve entering a tightening cycle, many investors have been downtrodden on the mREIT industry as a whole.

However, these investors may be overlooking two key points that could make Annaly quite attractive. First, the Fed isn't raising rates in an overheating economy. During the first quarter, U.S. GDP advanced a disappointing 0.5%, and inflation has been practically nonexistent save for a recent rebound in oil prices from 12-year lows. The Fed probably isn't going to have much room to raise rates quickly, or much at all, in the near term, which works in Annaly's favor since it benefits from lower lending rates. Annaly also holds nearly $30 billion in outstanding interest rate swaps, at a weighted average yield of 2.3%, that should continue to benefit from this slow-and-go strategy by the Fed.

The other key point here is that while Annaly does hedge against future rate hikes and has expanded its investments into non-agency-backed loans, the vast majority of its assets are tied up in agency-backed mortgage-backed securities. What this means is if the loan assets Annaly is holding go unpaid, either Fannie Mae or Freddie Mac step in to cover the difference. Agency-based MBSs may have lower yields than non-agency assets, but they're much safer. As of the first quarter, Annaly had $65.4 billion in agency-backed MBSs compared to only $1.2 billion in non-agency MBSs.

Valued nicely below its book value, Annaly's 11.2% dividend yield is quite the looker.

StoneMor Partners: 11.2% dividend yield

Among the services industry, StoneMor Partners (NYSE:STON) and its 11.2% dividend yield are worthy of income seekers' attention.

Image source: Pixabay.

StoneMor Partners is the owner and operator of 307 cemeteries and 104 funeral homes throughout 28 states and Puerto Rico. I know the idea of a "publicly traded death care company structured as a [limited] partnership" might sound a bit disturbing, but it's based on life's greatest certainty: our eventual expiration date. StoneMor's business would presumably be guaranteed to grow over time as the population of the United States expands. This basic-need service that StoneMor provides, and the clear pricing power that goes with it, is one reason it could be a smart long-term investment option.

StoneMor's long-term growth strategy also hinges on acquisitions of new cemetery plots and funeral homes, which is funded through operating cash flow and capital raises through unit offerings. These unit offerings can potentially dilute existing unitholders, so over the short term, acquisitions could be viewed as a negative. Over the long run, though, adding new plots and funeral homes increases its reach, which should add to profitability and cash flow. Based on StoneMor's first-quarter commentary, it anticipates stepping up its acquisition activity in the near term.

Last, we should understand that a lot of the recent weakness surrounding StoneMor's Q1 results -- a 5% decline in year-over-year cemetery contracts, and a 27% drop in comparable funeral home income on a year-over-year basis -- is weather related. The first quarter is often the toughest since weather prevents cemetery visits and preplanned plot purchases. A snowstorm or two is hardly a reason to get down on a business model that appears to be working very well. 

NGL Energy Partners: 11.6% dividend yield

Finally, investors looking for a high-yielding limited partnership in the energy sector should consider giving NGL Energy Partners (NYSE:NGL) their time of day.

Image source: NGL Energy Partners.

Before we go any further, let's freely admit that lower crude and natural gas prices over the past two years have hurt NGL Energy Partners just like every other company in the energy sector. In fact, NGL recently announced that it was cutting its quarterly dividend by 39%, to $0.39 per share, which still works out to a juicy 11.6% annual yield. But in spite of these woes, NGL Energy Partners has made all the right moves to secure its remaining distribution and return to growth in the near future.

Perhaps the biggest factor working in NGL's favor is its proactive effort to improve its balance sheet by paying down debt. In April, NGL announced a $200 million investment from Oaktree Capital Management that's to be used to repay borrowings from its revolving-credit facility. Compounded with the $170 million in annual cash NGL Energy Partners will get to keep now that it's lowered its dividend by 39%, and the $350 million from the sale of its general partner interest in TLP, you can see how quickly it'll be able to make a dent in its outstanding debt. The less debt NGL is carrying, presumably the more flexibility it'll have for reinvestment when the time is right. 

Another key point is that investors need to be able to look past a slew of one-time charges and benefits that won't be there following 2016. For example, impairment charges in NGL's water solutions business walloped the company with $358 million in operating losses in Q1. On the flip side, an increase in refined-product demand caused operating profits to soar in its refined-product and renewables segment. Once NGL is finished reorganizing its business, distribution growth is expected to return.

With the long-term outlook for energy still bright, NGL Energy Partners could be an attractive high-yield dividend to consider buying.