Some stocks just have it. What is "it"? A killer advantage that makes them dominant in their industry. 

Three healthcare stocks that definitely enjoy such an advantage are Illumina (NASDAQ:ILMN), Intuitive Surgical (NASDAQ:ISRG), and Teladoc Health (NYSE:TDOC). Here's what makes these stocks stand out from all the rest -- and why they're great long-term picks for investors to buy now.

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1. lllumina

When it comes to gene sequencing, no company has succeeded like Illumina has. The company's technology has enabled reducing the cost of sequencing a human genome from $20 million in 2006 to around $1,000 today. Over 90% of all gene sequencing performed to date was done using Illumina's systems. 

There are other companies that sell gene-sequencing systems. But Illumina's large install base gives it a substantial competitive advantage. So does the company's continual innovation. Illumina expects its NovaSeq platform, launched last year, will eventually help lower the cost of sequencing a genome to $100 or less. 

The tremendous cash flow generated from sales of its systems -- and, more importantly, consumables used in gene sequencing -- enables Illumina to keep plowing money back into more research and development. It also allows Illumina to make strategic acquisitions to stay on top. The company's recently announced buyout of Pacific Biosciences of California is a great example, as the deal will provide Illumina with a leading platform for long-read sequencing.

2. Intuitive Surgical

Intuitive Surgical pioneered the use of robotic assistance in performing minimally invasive surgeries. The company estimates that around 5 million surgeries have been performed using its da Vinci robotic surgical system since the first version of the system was cleared by the Food and Drug Administration in 2000. 

There are a couple of key advantages that Intuitive Surgical claims as a result of its years of expertise in robotic surgery. One is that no rival can come close to the safety track record that Intuitive has with da Vinci. Companies with newer surgical robot systems have a lot more convincing to do to win new customers than Intuitive does. This gives Intuitive Surgical a strong moat to defend its market share.

Another big advantage for Intuitive Surgical is that its customers have a financial incentive to maximize their return on investment. This means that they perform more procedures with the da Vinci system. That's music to Intuitive's ears since the company can count on a recurring and growing revenue source from selling replacement instruments. 

3. Teladoc Health

When it comes to providing telehealth services, there's one clear leader: Teladoc Health. The company counts around 40% of the Fortune 500, the largest U.S. companies, as customers. Teladoc has teamed up with more than 35 top health plans and over 290 hospitals and health systems. It landed a promising partnership with CVS Health to offer telehealth services through the pharmacy retailer's MinuteClinic walk-in clinics.

This momentum makes Teladoc hard to beat. The company's breadth and depth of services add to its strong competitive advantage. Its rivals typically offer more narrowly focused expert medical services and virtual urgent care services. Teladoc Health's products include a wide range of options, from general medical and pediatric care to behavioral health, dermatology, lab testing, and tobacco cessation.  

The company's rapid expansion into international markets and new virtual-care services makes Teladoc even more formidable. Teladoc Health claims the only global footprint in the industry, with operations in more than 125 countries thanks to its acquisition earlier this year of Advance Medical, the leading virtual-care provider outside the U.S. 

All great stocks to buy now

The really good news for investors is that all three of these stocks are still great picks to buy right now. 

Illumina should benefit from growth in the direct-to-consumer personal genomics services offered by companies like Ancestry.com and 23andMe, both of which are Illumina customers. The company has an even bigger opportunity from advances in personalized medicine and liquid biopsies to detect cancer at early stages.

Intuitive Surgical has long-term demographic trends working in its favor. Higher numbers of senior citizens should boost the numbers of procedures performed using da Vinci robotic surgical systems. Intuitive is also expanding the types of surgical procedures that can be done with robotic assistance.

Demographic trends should also help Teladoc Health. With aging populations across the world, governments and private payers are looking to ways to help control healthcare costs. Virtual care should provide an attractive alternative, which means that Teladoc should continue to enjoy strong momentum for years to come.

All three stocks are priced at a premium, though. That could make them more susceptible to steeper declines should there be any bumps in the road. Over the long term, however, Illumina, Intuitive Surgical, and Teladoc Health should be big winners.

Keith Speights owns shares of Illumina, Intuitive Surgical, and Teladoc. The Motley Fool owns shares of and recommends Illumina and Intuitive Surgical. The Motley Fool recommends CVS Health, Pacific Biosciences of California, and Teladoc. The Motley Fool has a disclosure policy.