Aurora Cannabis (ACB -3.02%) and Organigram Holdings (OGI -0.49%) have taken investors on a roller-coaster ride so far in 2018. Both marijuana stocks have experienced multiple swings of 10% or more. Both Aurora and Organigram also appear to be rebounding in recent days.

Which of these two Canadian marijuana growers is the better choice for investors now? Here's how Aurora and Organigram compare. 

Canadian red maple leaf image next to marijuana buds and a pack of cannabis cigarettes

Image source: Getty Images.

The case for Aurora Cannabis

Aurora Cannabis ranks as one of the two largest marijuana growers in the world, trailing only Canopy Growth. The company vaulted into this No. 2 spot thanks primarily to its acquisition of CanniMed Therapeutics this year. There are three key growth areas for Aurora that could make the stock attractive to investors.

First up is the company's current primary focus -- the Canadian medical marijuana market. Aurora has enjoyed strong sales growth, with revenue in its latest reported quarter more than tripling the total from the prior-year period. The domestic medical marijuana market is expected to increase by more than 200% within the next seven years.

But an even bigger opportunity that Aurora is already pursuing lies in the international medical marijuana market. The company is active in several countries that have legalized medical marijuana, the most important of which is Germany. Aurora's acquisition of CanniMed gives it exposure in several additional international markets. The company thinks that the international medical marijuana market will expand by a 21% compounded annual growth rate (CAGR) through 2025.

Turning back to Aurora's home front, Canada is on track to legalize recreational use of marijuana later this year. Professional services firm Deloitte estimates that the size of this market could be between $4.9 billion and $8.7 billion annually. Aurora continues to increase its production capacity to serve what is expected to be heavy demand, and it should have the second-largest capacity behind Canopy Growth. 

The case for Organigram Holdings

Organigram Holdings' market cap is only around one-tenth the size of Aurora's. But Organigram should have similar opportunities as its much larger rival.

The company has enjoyed strong growth in the Canadian medical marijuana market, with its number of active patients increasing by nearly sixfold between January 2017 and January 2018. Organigram received multiple honors at the Canadian Cannabis Awards in November, which should help the company position its products even more effectively in the domestic market.

Although Organigram lags behind Aurora and other larger marijuana growers in targeting international markets, the company could make up some of the gap in the future. In March, Organigram hired an experienced executive to run its new international division. Organigram CEO Greg Engel stated that the company intends to pursue opportunities in Europe, Australia, and other regions across the world.

Of course, the biggest immediate prize in front of Organigram is the recreational marijuana market in Canada. Construction is currently underway to increase Organigram's production capacity at its New Brunswick facility. This effort is expected to be completed in May and should enable Organigram to produce 36,000 kilograms per year. Further expansions are also planned that would give the company annual production capacity of 113,000 kilograms by April 2020.

Better pick

Aurora Cannabis is clearly better positioned to take advantage of both domestic and international opportunities. The company already generated more than one-fifth of its revenue in Germany in the last quarter. I think Aurora could enjoy strong sales growth in the German market as well as in Canada, especially once recreational marijuana is legalized.

On the other hand, Organigram's valuation looks more attractive than Aurora's does. My colleague Sean Williams thinks that Organigram could be the only "value marijuana stock" on the market right now. His analysis was based on Organigram's growth prospects, which could be tremendous. 

In my view, both of these stocks could be big winners over the next few years. If I had to only choose one, however, I'd go with Aurora. Its size could give the company an advantage in capturing market share. 

Keep in mind that both Aurora and Organigram face risks, though. There's a huge amount of growth baked into both stocks' prices. If demand isn't as great as expected -- or if supply ramps up so quickly that it outpaces demand -- Aurora and Organigram, like other marijuana stocks, could be in trouble.