It's no secret why income-seeking investors gravitate toward real estate investment trusts (REITs). Because REITs are required by law to discharge at least 90% of their profits in the form of dividends, they're a cash cow that investors love to milk.

Yet not all REITs are alike, and investing in them is not for everyone. Because so much of their earnings are devoted to dividends, very little is available to plow back into the business. That means capital appreciation won't be their top priority, so you aren't likely to find them on a list of fast-growing stocks.

If you understand the ground rules of REIT investing, though, then you're likely to find the following three right up your alley.

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AGNC Investment Corp.

Mortgage REITs (mREITs) like AGNC Investment Corp. (NASDAQ:AGNC) typically offer investors higher rates of return than other REITs, but they also come with more risks and carry more debt. Rather than invest in properties, mREITs like AGNC invest in mortgages and mortgaged-backed securities (MBS). Moreover, AGNC differentiates itself from many other mREITs by not originating mortgages, but by buying and selling government-backed mortgages packaged from Fannie Mae, Freddie Mac, and Ginnie Mae, so-called agency mortgages.

AGNC said net interest spread, net spread, and dollar roll income significantly improved last year to $2.70 per share, a 25% gain over the year-ago period, as the housing market heated up. Net interest spread and net spreads are the difference between the interest rate AGNC earns on its assets and the rate it pays on borrowings. Dollar roll is how much it makes by buying and selling forward mortgage contracts, or agreements to buy or sell an asset at a future date at a specified price. AGNC uses the proceeds from these transactions to finance its acquisition of agency-backed mortgage securities. The result of all these is essentially AGNC's net interest margin, or what would be operating margin for a non-financial firm.

Another key metric is constant pre-payment rate (CPR), which shows the percentage of AGNC's portfolio that the company expects to be paid off within a year. Lower is better, because a loan that's paid off doesn't produce interest for its holder, which can lead to lower rates of return.

Last year, low interest rates encouraged homeowners to refinance and pay off higher-rate mortgages early, which is why AGNC reported a 60% jump in its CPR to 17.6% in 2020. But as mortgage interest rates rose half a percentage point this year, AGNC's CPR fell to 11.3% at the end of the first quarter. Keeping an eye on which way rates are heading will help guide the direction CPR will take in future periods. We'll learn more when the company reports second-quarter earnings in the coming days.

AGNC ended the first quarter with $90.3 billion in total assets, 70% of which were agency mortgage-backed securities, while less than $2 billion worth were riskier credit-risk transfers and non-agency assets. That should give investors greater safety, and with its dividend yielding 8.9% at Friday's prices, AGNC Investment is a good choice for reliable and secure income streams.

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Annaly Capital Management

Annaly Capital Management (NYSE:NLY) is an mREIT in the same vein as AGNC, with almost 90% of its portfolio at the end of March parked in agency MBS. 

Annaly is the largest mREIT by market cap. So if you recently bought a house, there is a good chance your lender sold it to Fannie Mae or Freddie Mac, and Annaly could be holding it in its portfolio (AGNC, too, for that matter). Annaly also expects its long-term CPR to be in the 11% range, a significant improvement from the expected 17.7% rate last year. As noted above, mortgage interests play a leading role in the velocity of the CPR's rise or fall.

At the end of the first quarter, Annaly's total assets amounted to $100.4 billion, $92.6 billion of which was in agency securities. It also sold off its corporate real estate business, focusing on what it sees as the real growth market, residential mortgages. Like AGNC, Annaly is scheduled to report Q2 earnings in the coming days. 

The dividend yields 10.4% at Friday morning's prices and has generally averaged that since it went public back in 1997, though it has ranged as high as 22% and fallen as low as 3%. It has collectively paid more than $20 billion in dividends in that time, and with shares trading at a discount to its book value-- which, at 0.95, isn't too far from where the REIT typically trades -- Annaly Capital Management could be right for your long-term income needs.

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Realty Income

Realty Income (NYSE:O) is not an mREIT like AGNC and Annaly, but rather a commercial REIT that focuses on triple-net leases -- those where its tenants are responsible for taxes, maintenance, and insurance. More importantly, it develops single-tenant stand-alone buildings and enters into long-term leases with solid, financially stable tenants, over half of which are investment grade.

The investment-grade tenants were a rock for Realty Income during the pandemic. While it had to negotiate rent deferrals with some tenants during the crisis, that didn't take the same toll as the rent strikes other landlords had to manage. Collections from Realty Income's investment-grade tenants never dipped below 98%, and in fact by July they were already back at 100%, where they mostly stayed. The worst it saw was a dip to 82% for the total portfolio at the onset of COVID, but collections quickly bounded higher, and by July the portfolio was well above 90% again. These are typically recession-resistant businesses -- think discount stores, drugstores, and supermarkets.

Realty Income's average lease is almost 10 years long, and the properties are spread across 300 companies in 50 different industries, with no one tenant accounting for 10% or more of its revenue.

Like AGNC, Realty Income pays its dividend monthly (in fact, it calls itself The Monthly Dividend Company) and has made payouts to shareholders for 52 years, with over 600 consecutive payments in that time. Because it has also raised its dividend over 100 times, it is firmly ensconced as a Dividend Aristocrat, meaning it has hiked its payout annually for 25 years or more.

Realty Income's dividend yields 4% at recent prices, but its track record, stability, and tenant choice make it a unique REIT -- one that should arguably be a part of every investor's portfolio.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.