Which company ranks as the leader in developing a potential COVID-19 vaccine? Opinions will vary, but you can bet that AstraZeneca (AZN -0.67%) and Moderna (MRNA -1.69%) will be two of the most frequently mentioned drugmakers.

Both AstraZeneca and Moderna have delivered solid gains so far this year. Moderna stands as the bigger winner, with its share price more than quadrupling compared to AstraZeneca's year-to-date increase of 17%. But which of these coronavirus stocks is the better pick now?

Healthcare professional in mask and gloves, holding a vial labeled COVID-19 Vaccine with one hand and giving a thumbs-up with the other

Image source: Getty Images.

The case for AstraZeneca

What's the best argument for AstraZeneca being a better coronavirus stock than Moderna? Probably that AstraZeneca's COVID-19 vaccine candidate is only one of many potential growth drivers for the big pharma stock.

In the first quarter of 2020, AstraZeneca claimed seven products with sales growth percentages in the double digits. Four of those drugs generated year-over-year sales growth of more than 50%, with cancer drugs Tagrisso and Imfinzi leading the charge. And the seven didn't include fast-rising newer products such as blood-cancer drug Calquence.

AstraZeneca raked in sales of nearly $24.4 billion last year, with earnings of more than $1.3 billion. Wall Street analysts project the big drugmaker will increase its average annual earnings by 19% over the next five years, thanks to its strong current lineup and solid pipeline.

That pipeline includes over 60 programs pursuing additional indications for already-approved drugs. AstraZeneca claims 20 late-stage programs, notably featuring new asthma candidate tezepelumab and anemia candidate roxadustat.

But we can't overlook AstraZeneca's COVID-19 vaccine candidate. The company shrewdly teamed up with the University of Oxford earlier this year. The partners are now evaluating COVID-19 vaccine candidate AZD1222 in phase 2/3 clinical studies. World Health Organization chief scientist Soumya Swaminathan publicly stated that she thinks AZD1222 is probably the leading candidate among the more than 20 COVID-19 vaccines in clinical trials.

There's one other thing that investors should like about AstraZeneca: The company's dividend yields around 2.3%. If AstraZeneca's earnings grow as strongly as expected, future dividend hikes seem likely.

The case for Moderna

Moderna can't compete with AstraZeneca on financial performance or dividends. But the biotech claims one advantage that could make it a more attractive pick for many investors -- its relatively small size.

The fact is that success for Moderna's COVID-19 vaccine candidate mRNA-1273 would almost certainly be a bigger catalyst for the stock than success for AZD1222 would be for AstraZeneca. And that's because Moderna's market cap still hovers around $30 billion despite its huge gains this year, while AstraZeneca's market cap is nearly five times that.

Moderna's chances of success for mRNA-1273 are looking better and better. The New England Journal of Medicine published positive results last week from a phase 1 study of Moderna's COVID-19 vaccine candidate. Moderna expects to begin a phase 3 study on July 27.

Jefferies analyst Michael Yee thinks that mRNA-1273 could generate annual sales topping $5 billion if it's approved. That estimate doesn't seem unrealistic, considering the overall market opportunity for COVID-19 vaccines. But only looking at Moderna's prospects for mRNA-1273 shortchanges the biotech's potential.

If mRNA-1273 is successful, it should make Moderna's entire pipeline more attractive to investors. The company is currently evaluating a messenger RNA (mRNA) vaccine candidate for cytomegalovirus (CMV) in phase 2 testing. It has five other mRNA vaccine candidates in early-stage studies.

In addition, Moderna and Merck are developing two mRNA cancer vaccines, one of which is in phase 2 and the other in phase 1. Moderna is also partnering with AstraZeneca on a couple of mRNA therapies that are in phase 1 and phase 2 studies.

Better coronavirus stock

Which of these stocks is the better pick? It depends on your style.

If you're an aggressive growth investor, Moderna might be more attractive to you. Even with its remarkable rise in 2020, success for mRNA-1273 would likely cause the stock to move much higher.

On the other hand, more conservative investors should like AstraZeneca. The big pharma offers strong growth prospects along with a solid dividend. And AstraZeneca would fare much better than Moderna would if the companies' respective COVID-19 vaccine candidates flop.

I like both of these coronavirus stocks. But I think a greater number of investors will be more comfortable with AstraZeneca.