Neither Gilead Sciences (NASDAQ:GILD) nor Pfizer (NYSE:PFE) is expecting any sales growth this year. As a result, the market's already taken a swipe at both stocks, and they're starting to look like a bargain.

Both of these drugmakers have products that throw off huge cash flows, and they're committed to delivering as much of their profit to shareholders as possible. Here's a side-by-side comparison to find out which one can probably deliver the most.

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The case for Gilead Sciences

Gilead Sciences isn't expecting any top-line revenue growth in 2019 because expiring U.S. patents for Letairis and Ranexa could lead to a loss of around $1.2 billion. The company also expects around $900 million in lost sales because of competition with AbbVie (NYSE:ABBV) for a share of a hepatitis C antiviral (HCV) market that's been steadily shrinking. Total HCV sales plummeted from $9.1 billion in 2017 to just $3.7 billion in 2018, and Gilead's new cellular cancer therapy, Yescarta, is proving more difficult to sell than anticipated.

On the plus side, Gilead's new single-tablet HIV regimen, Biktarvy, is beating expectations. Sales of the drug hit an annualized $2.3 billion run rate during the last three months of 2018, which was only the third full quarter since its U.S. launch. Last year, EvaluatePharma predicted that Biktarvy sales would reach $6.1 billion annually by 2024, and at this rate, it will meet that deadline early. 

Unlike HCV, HIV still can't be stamped out completely and patients need to take an antiviral for the rest of their lives. In the U.S., and more recently Germany, Biktarvy's already become the most commonly prescribed HIV regimen for people switching to a new antiviral, and for those taking one for the first time.

In the first half of 2019, Gilead will present phase 3 data from two new drugs that could drive the stock higher. The company's most advanced non-alcoholic steatohepatitis (NASH) candidate, selonsertib, recently failed to help patients with advanced cirrhosis significantly reduce liver scarring. Another NASH study with less severely affected patients could put the selonsertib program back on track when Gilead reads out the results during the second quarter. Since there aren't any available treatments for millions of patients with NASH, an eventual approval for just a limited percentage of the overall population could lead to blockbuster sales.

Check out the latest Gilead earnings call transcript.

Gilead's experimental tablet for rheumatoid arthritis, filgotinib, is far behind its potential competitors on the development timeline, but it's winning in the safety department. Gilead will report data from two pivotal filgotinib studies during the first quarter, and if its safety profile remains untattered, it could earn more than $5 billion annually at its peak.

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The case for Pfizer

America's largest pharmaceutical company thinks the upcoming loss of market exclusivity for Lyrica will lop $2.6 billion off its top line this year. Despite the impending loss, Pfizer expects sales and adjusted earnings to remain flat in 2019.

Once pain from ripping off the Lyrica bandage subsides, Pfizer won't have to offset losses from another big product until at least 2026. Pfizer has a lot of moving pieces that generated $53.6 billion in revenue last year, and pulling the entire train uphill isn't easy. With a handful of potential growth drivers on the horizon, though, Pfizer could start growing by double digits again in a couple of short years. 

An impressive four new cancer drug approvals during the last four months of 2018 will bolster an oncology segment that seems unstoppable. Sales of the company's breast cancer drug, Ibrance, surged 58% during the fourth quarter to an annualized $4.5 billion, and recently approved Talzenna could perform just as well as a treatment for newly diagnosed breast cancer patients harboring BRCA mutations.

Daurismo could become a blockbuster blood cancer therapy as an important new option for older adults newly diagnosed with acute myeloid leukemia who are too frail to handle standard chemotherapy at an effective dosage. Adding Daurismo to low-dose chemo decreased patients' risk of death by 54% compared with low-dose chemo on its own. 

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Running the numbers

At recent prices, Gilead's stock trades at just 10.2 times forward earnings expectations, plus it offers a juicy 3.7% dividend yield. Pfizer's stock has been trading at a slightly higher price 14.5 times earnings expectations, and its dividend yield of 3.4% is a bit lower. Both of these companies produce an enormous profit that keeps their dividends well funded, and we should see some payout bumps in the years ahead.

Gilead's hepatitis sales have probably reached a bottom, and as a smaller company, it won't be quite as hard for Gilead to push the needle forward. Both stocks are tempting, but Gilead probably has a better chance to deliver market-beating gains. That makes it the better buy today.

Editor's Note: This article has been updated to reflect Gilead's phase 3 selonsertib study outcome.