Why make investing harder than it needs to be? Sometimes the best stocks really are large-caps with a valuation of $10 billion, or higher. Large-cap stocks might seem played out, but they almost always have established business models that can stand the test of time, which means you can rest easy at night. 

With this in mind, we asked three of our Foolish contributors to name one large-cap stock they believed investors should consider adding to their portfolios for the long term. Jumping to the top of the list were biotech blue-chip Celgene (CELG), do-it-yourself auto parts retailer AutoZone (AZO 1.02%), and robotic surgical device manufacturer Intuitive Surgical (ISRG 1.16%)

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The biotech stock to cure your long-term concerns 

Sean Williams (Celgene): One large-cap stock that seemingly has it all for long-term investors is biotech blue-chip Celgene, which is primarily a developer of cancer and anti-inflammatory drugs.

Arguably the biggest allure for Celgene, and also its most notable risk, is the company's multiple myeloma drug, Revlimid. Revlimid has been growing at a blistering pace of 15% to 20% per year and is forecast to continue to do so again in 2017 with a conservative projection of $8 billion to $8.3 billion in full-year sales. Revlimid has benefited from longer duration of use, an uptick in multiple myeloma diagnoses (which is a function of a growing population and improved diagnostic testing), strong pricing power, and leading market share. The flip side to this is that Revlimid accounts for more than 60% of Celgene's current sales, meaning when it does lose its patent protection, Celgene, and its shareholders are going to feel it.

Now, back to the good news. In December 2015, Celgene worked out a settlement with a handful of generic drug developers that were looking to bring generic versions of Revlimid to market. The settlement allows Natco Pharma to bring a limited supply to market beginning in March 2022, but it'll keep a majority of generic development off of pharmacy shelves until the end of January 2026. In effect, Celgene gave its lead drug a 10-year runway to grow sales and generate insane amounts of cash flow.

In the meantime, Celgene is reinvesting in its business via collaborations and acquisitions. Its purchase of Receptos for $7.2 billion in 2015 allowed it to gain hold of promising next-generation multiple sclerosis drug ozanimod, which also has the potential, if approved, to expand its label to ulcerative colitis, too. Celgene's management team believes ozanimod may have $4 billion, or more, in peak sales potential.

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Celgene also has dozens of collaborations, many of which are for first-in-class cancer therapeutics. Though these collaborations could result in Celgene paying out big sums of money in development, regulatory, and sales milestones, it also allows the company to focus its spending on its most promising partnered compounds. 

Despite its $90 billion-plus market value, Celgene has the potential to grow by 10% or more for years to come. As it diversifies its pipeline away from Revlimid with the hopeful introduction of ozanimod, label expansions for oral anti-inflammatory drug Otezla, and perhaps a few successes from its numerous collaborations, Celgene's attractiveness may continue to grow.

Selling at a discount

Daniel Miller (AutoZone): One smart pick for a long-term stock, so that investors can better ride out a cyclical auto industry and how it impacts the company, AutoZone, Inc. As many are aware, AutoZone is a leading seller of aftermarket automotive parts, tools, and accessories to the do-it-yourself (DIY) consumer, with a recent focus on growing its business through the do-it-for-me segment of consumers. What's appealing about AutoZone's stock right now is that it's offering a discount for the first time in years, as 2017 has slashed the company's value by about 25%.

AZO Chart

AZO data by YCharts.

To be fair, AutoZone recorded a more challenging spring selling season than management had anticipated, and it showed during the third-quarter results. The company's net sales of $2.6 billion during the third quarter was a meager increase of 1% compared to the prior year, and domestic same-store sales declined 0.8% during the same timeframe.

But part of the issues is short term in nature, including the slight decline in gross margin due to higher supply chain costs associated with management's inventory initiatives. Those initiatives were increasing the number of weekly parts deliveries to its stores, so the company could focus on increasing commercial (do-it-for-me) sales, which require a larger assortment of parts available. However, management didn't find enough benefit in increasing the shipments and will dial back the weekly deliveries to stores with fewer commercial sales to help bump margins back up.

Over the long term, its supply chain costs from the past quarter shouldn't be an issue, and the focus on increasing the company's commercial sales is still imperative as vehicles continue to become more complex and consumers increasingly need repairs done for them. AutoZone has proven over the course of its history that it's committed to returning value to shareholders through large share buybacks and that it can grow organically as well as successfully implement acquisitions. If you're looking for a long-term stock, this is a solid option to consider.

An operating room with a digital heart monitor in the forefront.

Image source: Getty Images.

5 reasons to own this robotic surgery specialist

Anders Bylund (Intuitive Surgical): Let me give you the top five reasons I own shares of Intuitive Surgical -- and intend to hold on to those shares for the long run:

  1. The robotic surgery veteran competes mainly with traditional, unassisted surgery methods. There is little direct competition going on, here.
  2. Many companies have stated their desire to enter the robotic surgery market, but Intuitive Surgical has surrounded its chosen field with strong technology patents -- and a tendency to buy out would-be rivals who seem to be getting close.
  3. The company is not content to rest on its laurels. Over the last four quarters, Intuitive Surgical funneled more than 9% of its revenues into more research and development, up from just 7.5% two years ago. The R&D-to-revenue ratio is moving in the right direction.
  4. If the development budget seems hefty, Intuitive Surgical's trailing free cash flows have soared from $550 million to $960 million over the same period. The company is not digging into its cash reserves, here, but is growing its cash balances quickly.
  5. If Intuitive Surgical's future as a fast-growing business is in danger at all, it would be because even larger medical players are chomping at the bit to enter this market. That paints a large buyout bullseye on the company's back, even with a $33 billion enterprise value and strong upward share price momentum.

For all of these reasons, I'm more than comfortable holding on to my Intuitive Surgical shares for at least the next decade. It's a good idea to keep tabs on the competition, and on the company's beefy financial results, but there is nothing wrong here as of mid-2017.