Moderna (NASDAQ: MRNA) and BioNTech (NASDAQ: BNTX) just may be the most talked about biotech stocks on the planet these days. Why? They both developed and are selling the first coronavirus vaccines. BioNTech is the partner of big pharma company Pfizer. Moderna and BioNTech have climbed 125% and 175%, respectively, in the first half. To predict which may be the best choice for the second half, let's play a game. It's called Motley Fool CAPS. And it uses the wisdom of crowds to identify smart investments. How does CAPS work? Thousands of players predict which stocks will lag behind or surpass the S&P 500 over a certain time frame. The game rates players based on the percentage of people they're outperforming. It rates stocks based on the number of players who've picked that stock to outperform. Players with higher ratings have more influence on a stock's rating -- so CAPS gives the opinions of investors with a strong track record more weight. Let's see what CAPS tells us about Moderna and BioNTech. Image source: Getty Images. Moderna CAPS rating: 4 out of 5 stars What investors might be noticing: Moderna successfully brought its coronavirus vaccine candidate from trials to market in less than a year. The vaccine -- Moderna's first commercialized product -- has already brought in more than $1 billion in quarterly profit. And the company expects vaccine sales of around $19.2 billion this year. What's holding Moderna back from a better score: Moderna is discussing possible 2022 orders with all of the countries that bought doses this year. It's still unclear whether vaccine revenue next year will top that of this year. If it does, investors may reward Moderna with a fifth CAPS star. BioNTech CAPS rating: 5 out of 5 stars What investors might be noticing: BioNTech is the developer of the Pfizer vaccine. The two companies are splitting billions of dollars in vaccine revenue. Total signed contracts as of May represent $14.7 billion for BioNTech alone. So far, the Pfizer/BioNTech product has fully vaccinated more than 84 million people in the U.S., for the biggest share of that market. The companies also are major suppliers to the European Union -- and recently signed a deal to provide 1.8 billion vaccine doses through 2023. This European commitment beyond 2021 may give BioNTech an edge when it comes to investor confidence. It ensures a high level of revenue beyond this year. Foolish bottom line Four-star stocks and five-star stocks are pretty much on par when it comes to performance. Over the past year, 77% of five-star stocks and 78% of four-star stocks delivered double-digit gains or better. Of course, it's essential to study a company's fundamentals before making an investment decision. But if we consider CAPS alone, it looks like Moderna and BioNTech may both extend their winning streak in the second half. 10 stocks we like better than BioNTech SEWhen our award-winning analyst team has a stock tip, it can pay to listen. After all, the newsletter they have run for over a decade, Motley Fool Stock Advisor, has tripled the market.* They just revealed what they believe are the ten best stocks for investors to buy right now... and BioNTech SE wasn't one of them! That's right -- they think these 10 stocks are even better buys. See the 10 stocks *Stock Advisor returns as of June 7, 2021 Adria Cimino has no position in any of the stocks mentioned. The Motley Fool recommends Moderna Inc. The Motley Fool has a disclosure policy.Source