What's a six-letter word that's guaranteed to make investors happy? Growth. While growth comes in several flavors, they're all interrelated. Growth in revenue helps make earnings growth possible, and earnings growth tends to drive stock prices higher.

There are lots of growth stocks on the market. Which rank among the best? I'd put Ligand Pharmaceuticals (NASDAQ:LGND), Veeva Systems (NYSE:VEEV), and Vertex Pharmaceuticals (NASDAQ:VRTX) high on the list. Here's why these are three growth stocks I'd buy right now. 

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Ligand Pharmaceuticals

Ligand Pharmaceuticals' primary focus is on technologies that help other drugmakers discover and develop medicines more effectively. The two most important such technologies in Ligand's product lineup are Captisol and OmniAb. Captisol is a modified chemical structure that helps improve solubility, stability, bioavailability and dosing of active pharmaceutical ingredients (APIs). The OmniAb platform consists of several fully human antibodies that help improve manufacturability and therapeutic efficacy as well as reduce immunogenicity for drugs in development. 

What I really like about Ligand's business model is the diversification it brings. Thirteen products are already on the market that use the company's platforms, most notably multiple myeloma drug Kyprolis and bone marrow stimulant Promacta. But there are dozens of other programs in Ligand's pipeline, including two currently awaiting approval and eight in late-stage development. 

Analysts project that Ligand will grow earnings by more than 27% annually over the next five years. With its robust pipeline, that level of growth seems attainable. While the stock is up more than 25% year to date, a recent pullback presents a good buying opportunity, in my view.

Veeva Systems

Veeva Systems is essentially a Salesforce.com (NYSE: CRM) for the life sciences industry. In fact, Veeva uses Salesforce's platform for some of the cloud-based customer relationship management (CRM) applications that it markets. 

Although Veeva has grown rapidly over the last few years, there remains a tremendous opportunity for the company in its core life sciences market. Veeva has tapped less than 5% of the potential market. The company also continues to roll out new products that are attractive to existing customers. Another big plus for Veeva is that it's expanding beyond life sciences. Veeva landed a major consumer packaged goods customer earlier this year and hopes to gain even more traction in industries outside of its core market in the future. 

Can Veeva keep up its fast-and-furious growth rate that has led to the stock soaring more than 40% so far in 2017? Probably not. However, the consensus among Wall Street analysts is that the company will grow earnings by close to 22% annually in the coming years.  

Vertex Pharmaceuticals

Vertex Pharmaceuticals has made a name for itself in treating cystic fibrosis, a relatively rare genetic disease that can cause damage to the lungs and the digestive system. The company has two CF products on the market -- Kalydeco and Orkambi. Vertex withdrew hepatitis C drug Incivek from the U.S. market a few years ago in the face of new therapies that cured the disease.

While sales for Kalydeco and Orkambi continue to increase, the real promise for Vertex comes from its pipeline. The company expects an approval decision from the Food and Drug Administration on a combination of tezecaftor and ivacaftor (Kalydeco) in treating CF by Feb. 28, 2018. Vertex also will initiate late-stage studies for triple-drug combinations for treating CF early next year. I expect these more powerful therapies will significantly expand the market for Vertex.

Analysts agree with this positive outlook. The average analysts' estimate for Vertex's annual earnings growth over the next five years is a whopping 65%. It's not surprising that the stock is up close to 90% year to date.

Best pick?

You've probably figured out which of these three stocks is my pick as the best of the group. I like Ligand's diverse pipeline. I think Veeva Systems has a great moat and plenty of room to run. But it's hard to beat the growth prospects for Vertex.

The company has a nice head start over other potential rivals in the CF market. Vertex is also looking at exploring treatments for other genetic diseases. Vertex ranks as one of my five favorite biotechs on the market right now. Like I said earlier, growth is guaranteed to make investors happy.

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.