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One of my favorite Warren Buffett quotes is "Our favorite holding period is forever," and I try to apply this wisdom to my own portfolio. There are many good reasons to sell a stock, but I like to go into every investment with the intention of holding on to the stock forever. With that in mind, here are three "forever stocks" that I have no intention to ever sell.

A great business model, and strong dividend history
Buffett has said that people should buy stocks because they want to own the business, not because they want the stock to go up. Toronto-Dominion Bank (TD), or simply "TD Bank," is a business I want to own.

TD Bank is based in Canada and also has a rather large (and growing) U.S. branch network, built on the philosophy of being "America's Most Convenient Bank." While other big banks are closing branches and scaling back on the in-person services they provide, TD is doing the opposite. Its branches are open late at night and on weekends (even Sundays), and you can even bring your dog with you to do your banking.

The bank is making sure that it expands its branch network in a cost-effective and sustainable manner. Newer branches are significantly smaller than old ones, require 32% fewer full-time-equivalent workers, and cost 34% less to operate. In addition to the growth of the branch network, TD has other ambitious plans, such as adding $500 million in new credit card revenue over the next several years, and double-digit annual growth in its wealth-management business.

Over the past decade, TD Bank has handily outperformed the overall North American banking sector and has increased its dividend at an impressive 12% average annual rate. In short, the reason I want to own TD forever is that it has an outstanding business model, and I believe the strong investment performance will continue because of it.

Dominance in a beaten-down industry
As oil prices have collapsed, energy stocks have plummeted. Times like these are great opportunities to buy the long-term winners at low prices, which is why I recently loaded up on National Oilwell Varco (NOV 0.06%).

National Oilwell Varco sells equipment and technology to the oil drilling equipment. It has a dominant 80% share of the offshore drilling market, and a majority of the world's larger land-based rigs also use components the company manufactures. Plus, National Oilwell Varco's standardized rig designs mean that it will have a steady stream of repeat business for spare parts.

Nobody knows what oil prices will do, and the past year has proved me wrong several times about what the price of oil "can't" do. However, I can say with near certainty that sub-$30 oil prices aren't going to last forever, and even though it may take years, National Oilwell Varco's business should rebound nicely. In the meantime, it is well positioned to ride out the tough times, and it pays a dividend yield of more than 6% while I wait.

Invest with the best
One of my favorite stocks in the market is and always will be Berkshire Hathaway (BRK.A -2.04%) (BRK.B -1.96%), even though Buffett has warned investors not to expect the performance of the past 50 years to continue.

While Berkshire may be getting to a point where the expectation of 20% annual returns is unreasonable, there are still some compelling reasons to own it in your portfolio.

Most significantly, Berkshire owns 60 subsidiary companies in a variety of industries, from insurance to food products to private jets. And the company has a stock portfolio that reads like a "who's who" of rock-solid companies. Among Berkshire's largest stock holdings are Wells Fargo, AT&T, Coca-Cola, IBM, and Procter & Gamble, just to name a few. Essentially, Berkshire Hathaway is a smart way to acquire a well-diversified investment portfolio with a single stock.

At the low end of its historic valuation, Berkshire is a compelling investment I plan to hang onto forever, and I may even buy more if the low prices persist.