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You don't want to go buy just any big pharma stock. Some are definitely better than others. But figuring out which big pharma stock to go with requires checking out the companies' product lineups, pipelines, and financial health. Digging into those details is exactly what's required in a head-to-head matchup between Pfizer Inc. (PFE 0.91%) and GlaxoSmithKline plc (GSK 0.67%). Here's how the two drugmakers' stocks compare.

The case for Pfizer

Pfizer's current product lineup probably merits an overall grade of B+ or maybe even an A-. Total revenue increased 15% in the first half of 2016 compared to the prior-year period. Lyrica remained especially strong, generating sales of over $2 billion during the period -- up 17% year over year.

Other current products helping Pfizer significantly include smoking cessation drug Chantix/Champix and cancer drug Xalkori. The biggest rising star in the company's lineup is another cancer drug, Ibrance. Sales for Ibrance in the first six months of this year jumped to $942 million from $178 million in the prior-year period. That's not an apples-to-apples comparison, though, since Ibrance gained FDA approval in February 2015.

What about Pfizer's pipeline? I'd give it a grade of A, if nothing else for its depth. Pfizer's pipeline includes 92 clinical studies. Nine drugs are awaiting regulatory approval. Some of those are existing drugs on the market for which Pfizer is trying to win approval for a new indication, such as seeking to win a thumbs-up for Xeljanz in Europe for treating rheumatoid arthritis. Others are new drugs, including atopic dermatitis treatment crisaborole. 

Twenty-nine of the 92 studies are in phase 3. That's an exceptionally strong late-stage candidate pool. Several of these phase 3 drugs should have a good chance of becoming blockbusters if approved. I'd include PCSK9 inhibitor bococizumab in that group, along with diabetes drug ertugliflozin, cancer drug avelumab, pain medication tanezumab, and perhaps a few others.

As for financial health, Pfizer appears to be in good shape. My grade on this front is an A-. Pfizer's revenue and earnings are growing. The company reported nearly $21 billion in cash, cash equivalents, and short-term investments at the end of June.

The only thing I'm not so crazy about with Pfizer's financials is the company's debt of over $44 billion. Pfizer has been on a buying spree lately, acquiring Anacor and Medivation this year. The company hasn't exactly been a bargain shopper, paying premium prices for both biotechs. 

Investors should like Pfizer's dividend, which currently yields 3.67%. The main concern about that dividend, though, is Pfizer is shelling out more than its total earnings to pay it. That can't go on indefinitely. Pfizer should be able to grow earnings enough to avoid a dividend cut, but it's entirely possible that the company might have to disappoint shareholders in the future by reducing its dividend, particularly if it keeps on its acquisition spree. 

The case for GlaxoSmithKline

GlaxoSmithKline's current product lineup looks OK, but not great. I'd give Glaxo a grade of C in this area. Total revenue in the first half of 2016 increased by 5%. There are some solid winners among current products, including respiratory drugs Anora Ellipta and Relvar/Breo Ellipta along with HIV drug Triumeq. Several of Glaxo's vaccines are also going really well, especially pneumococcal vaccine Synflorix and type B meningitis vaccine Bexsero. 

The problem for GlaxoSmithKline, though, is that sales are slipping for several of its biggest drugs. Respiratory drug Seretide/Advair is the drugmaker's top-selling pharmaceutical, but sales fell 16% year over year in the first half of 2016. Likewise, Glaxo's biggest vaccines, Infanrix and Pediarix, saw sales drop by the same percentage during the period.

Better news could be on the way for the company, though. Glaxo's pipeline includes over 100 clinical studies. I give the drugmaker an A when it comes to pipeline potential. 

Glaxo's pipeline includes 15 drugs and vaccines in late-stage studies. An HIV treatment regimen combining Tivocay and Gilead Sciences' Odefsey looks promising. So does respiratory drug mepolizumab and autoimmune disease drug sirukumab.  

On the financial front, Glaxo probably deserves a grade of B-. Revenue is growing, albeit slowly. Glaxo reported a net loss in the first and second quarters of 2016, however. The drugmaker reported cash, cash equivalents, and liquid investments totaling $4.7 billion at the end of June. Glaxo's debt stood at $19.6 billion. 

You won't find too many healthcare companies with a higher dividend yield than Glaxo. The drugmaker's dividend yield currently stands at 4.48%. The problem, though, is that Glaxo doesn't have the profits to keep paying this nice dividend. There's a significant risk that the company will have to cut its dividend at some point.

Better buy

If you've kept track of the grades for both of these big pharma companies, you probably already know which stock I think is the better buy. Pfizer wins pretty easily.

Pfizer isn't a perfect choice for investors. The company's legacy drugs weigh down overall performance. Pfizer recently decided not to spin off a separate company, so nothing will change anytime soon on this front. There's also risk that some of its pipeline drugs will run into problems. And Pfizer needs to put the brakes on high-price acquisitions to keep from running its debt up even more.

All that said, Pfizer remains a good pick for investors with a long-term perspective. Revenue and earnings should keep growing. The dividend seems to be relatively safe. Between GlaxoSmithKline and Pfizer, I think Pfizer is clearly the better buy.