Lots of companies market products that help individuals manage diabetes. Abbott Laboratories (NYSE:ABT) and Novo Nordisk (NYSE:NVO) rank as two of the biggest of these companies in the diabetes arena. But neither Abbott nor Novo Nordisk focuses exclusively on diabetes.

Both stocks have underperformed the S&P 500 index so far this year. However, both stocks also have solid growth opportunities. Which is the better pick for long-term investors? Here's how Abbott and Novo Nordisk stack up against each other.

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The case for Abbott Labs

Probably the strongest argument for investing in Abbott Labs is the diversification it provides. Granted, one stock focused on only one sector isn't a textbook example of diversification. However, Abbott operates four business segments in different areas of healthcare, each of which generates billions of dollars in annual revenue.

Abbott's medical devices segment stands out as its biggest moneymaker. The segment raked in close to $3.1 billion in sales in the third quarter, with especially strong growth from its HeartMate 3 left ventrical assist device and its MitraClip device used for the treatment of mitral regurgitation.

There's one important medical device marketed by Abbott that wasn't included in its medical devices segment revenue total, though: Freestyle Libre. Sales for the continuous glucose monitoring (CGM) system totaled $463 million in Q3, up a whopping 63% year over year. It's taking longer than Abbott expected to win U.S. Food and Drug Administration (FDA) approval for a new version of Freestyle Libre. But assuming that approval isn't derailed, the new product should be a huge growth driver for Abbott. 

Although Abbott spun off a large part of its pharmaceuticals business with the creation of AbbVie in 2013, the company retained an established pharmaceuticals segment. This unit continues to enjoy solid growth in emerging markets, particularly in Brazil, China, and India. Abbott's established pharmaceuticals segment should be able to deliver sustained long-term growth as these emerging markets develop.

The company's diagnostics and nutrition segments don't generate as impressive growth as its other businesses do. However, Abbott's Alinity family of lab instruments continues to stand out as a top growth driver. Pediatric nutrition sales in the U.S. are also growing briskly, albeit overshadowed to some extent by challenges in Asian markets, particularly China.

Overall, Abbott Labs should be able to deliver double-digit percentage earnings growth for years to come, with Freestyle Libre, MitraClip, and Alinity leading the way. The company also pays a dividend that currently yields nearly 1.6%. This dividend, combined with Abbott's solid growth prospects, should translate to attractive total returns for investors over the long term.

The case for Novo Nordisk

Novo Nordisk has been a longtime leader in the diabetes drug market. The Denmark-based drugmaker began producing insulin more than 90 years ago and has since introduced multiple blockbuster non-insulin diabetes drugs. 

Today, Novo Nordisk's biggest challenge is that its insulin products face pushback from insurers over pricing. The result was that total insulin sales for the company slipped 2% year over year in the second quarter. The good news for Novo Nordisk, though, is that its other products more than made up for the decline in insulin revenue.

Novo Nordisk's biggest winner right now is type 2 diabetes drug Victoza. But sales for GLP-1 receptor agonist Ozempic are growing fast. And Novo Nordisk has a new GLP-1 drug, Rybelsus, that's a tablet form of Ozempic that's taken daily. This new drug just might become the company's top winner over the next few years.

While Novo Nordisk's primary focus is on diabetes, the company targets other indications as well. For example, the company won FDA approval for Saxenda in late 2014 as a treatment for obesity. Novo Nordisk is partnering with Gilead Sciences to evaluate Ozempic in combination with Gilead's cilofexor and firsocostat in treating nonalcoholic steatohepatitis (NASH).

In addition, Novo Nordisk markets five drugs that treat hemophilia, including NovoSeven. The company also sells multiple human growth hormone and hormone replacement therapy products.

Wall Street analysts think that Novo Nordisk will grow its earnings by an average of nearly 11% annually over the next five years. With the company's dividend yielding nearly 2.4%, Novo Nordisk appears to be in a strong position to provide great total returns for investors.

Better buy

Both of these healthcare stocks have plenty to offer investors. But I think that Abbott Labs is the better choice.

Abbott's diversification across multiple fronts in healthcare gives it a distinct advantage, in my view. If one area encounters challenges, other areas can make up the slack. That's exactly what's happening right now for the company, with the weakness for its nutrition business being more than offset by strength in its other segments.

I think that the new version of Freestyle Libre will be a huge success for Abbott. I also expect the company's relentless focus on innovation will pay off with new products over the next few years. Abbott Labs looks like a winner over the long run.