Now is a great time to get in on biotech growth stocks. Many of them are trading lower than in the past -- yet, at the same time, they're closer than ever to reaching the commercialization of key products. And these potential products may drive blockbuster revenue over the long haul.

Two terrific examples of growth stocks to buy today are coronavirus vaccine maker Moderna (MRNA 0.02%) and gene editing expert CRISPR Therapeutics (CRSP -0.76%). They have what it takes to become multi-product companies in a few years -- and earnings growth and share performance should follow. If you could only choose one, which is the better buy right now? Let's find out.

The case for Moderna

Some investors have worried that Moderna's best days may be in the past. The company's one and only commercialized product is the coronavirus vaccine -- and vaccine demand is declining. That product brought in billions in earnings over the past two years.

But Moderna may actually be at the very start of its growth story. Yes, we are likely to see vaccine revenue -- and, therefore, total revenue -- decline in the near term.

But the company has plenty of pipeline programs that could deliver new blockbusters in the next few years. The closest to market are vaccine candidates for the respiratory syncytial virus (RSV), flu, and cytomegalovirus (CMV), which are all in phase 3 studies. Moderna recently reported positive data from the RSV trial and aims to file for regulatory approval in the first half of this year -- which could lead to commercialization as soon as early next year.

If even a handful of the 38 candidates the biotech has in clinical trials makes it to commercialization, Moderna could become a multi-product company in the not-too-distant future.

Meanwhile, Moderna expects the post-pandemic coronavirus vaccine market to mimic that of the flu. That means it could remain in blockbuster territory even if vaccine revenue falls. Moving forward, the vaccine and new products may spur a big phase of growth for Moderna.

The case for CRISPR Therapeutics

CRISPR has reached its most exciting moment yet. The biotech company and partner Vertex Pharmaceuticals recently completed regulatory submissions for exa-cel, their gene-editing candidate for blood disorders, in the U.K. and Europe. They aim to complete a U.S. submission by the end of the first quarter. If approved, exa-cel would be CRISPR's first product.

The idea of launching a first product is positive. But what's even better is that exa-cel could become a blockbuster. For a couple of reasons. First, the blood disorders it treats -- beta-thalassemia and sickle cell disease -- currently have limited treatment options. Second, exa-cel is designed as a one-time curative treatment. So doctors and patients will probably be eager to give it a try.

Initially, CRISPR aims to win approval in the adult population. But the company is studying the candidate in children in phase 3 trials. If all goes well, approval for kids could broaden the commercial opportunity for this treatment.

CRISPR also is making solid progress with CTX-110, an immuno-oncology candidate. The company recently reported positive safety and efficacy data from an earlier clinical trial. It's since started a phase 2 trial that could support a regulatory submission.

So if all goes well, CRISPR could launch two products in the not-too-distant future. And from that point, earnings and the share price may take off.

Moderna or CRISPR?

Now, let's take a look at share price. Both stocks dropped in the double digits last year -- Moderna fell 29%, and CRISPR lost 46%. Considering future growth, they are both ripe for a rebound. But which stock offers the best entry point right now?

Investors may want to get in on CRISPR first. Regulatory decisions on exa-cel may be on the horizon. A potential nod and sales to follow could push the shares higher from today's level.

Moderna's potential catalysts -- for example, regulatory review of its RSV candidate -- are a bit farther down the road. And declines in vaccine demand may continue to weigh on Moderna shares in the near term.

So if I could buy just one of these stocks today, I would go for CRISPR. But both innovative biotech companies may be winning investments over the long term.