Popular ideas aren't always good ideas. That's true with trends (remember how eating Tide Pods went viral?), and with stocks (recall that scandal-plagued Enron was once a favorite stock among investors).

On the other hand, just because an idea enjoys widespread popularity doesn't automatically mean that it isn't good. As a case in point, there are quite a few stocks that rank among the 100 most popular on the Robinhood trading platform that look like great picks. I think that buying three of them, in particular, would be a really smart move right now.

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1. Amazon

Amazon.com (NASDAQ:AMZN) isn't just popular on Robinhood. It has a market cap approaching $1.7 trillion, so it's obvious that many more investors like the tech stock. But this e-commerce giant isn't finished growing.

My Motley Fool colleague Dan Sparks recently made a really good argument as to why Amazon could be poised for a huge fourth quarter. Dan noted that Amazon's members-only sales event Prime Day is likely to generate tremendous sales in Q4. He thinks those sales will come on top of the company's nice head of steam fueled by the COVID-19 pandemic. Dan is exactly right, in my view.

Even though e-commerce has been around for several decades, it's easy to overlook just how much growth potential remains. The U.S. Census Bureau recently reported that e-commerce sales in the second quarter of 2020 accounted for only 16.1% of total retail sales.

Investors also can underestimate Amazon's growth potential by focusing too much on its e-commerce business. The company ranks No. 1 globally in the fast-growing cloud-hosting market. Amazon has also expanded into new areas, including groceries, healthcare, and self-driving car technology, all of which should pave the way for additional growth in the future.

2. PayPal

PayPal Holdings (NASDAQ:PYPL) is another popular Robinhood stock that is well-positioned to benefit from the ongoing e-commerce boom. The fintech stock has even narrowly outperformed Amazon so far this year.

I suspect that PayPal will have great news in a few weeks when it reports its third-quarter results. The company posted strong revenue and earnings growth in Q2. It even recorded its best quarter ever for net new active accounts added.

One thing that I really like about PayPal is its continual innovation. Just over the last few months, the digital payments leader has launched multiple new products that should spur sales growth, including QR code functionality for cashless in-store purchases. Earlier this month, PayPal unveiled its first Venmo credit card.

Speaking of Venmo, the peer-to-peer (P2P) payment app is one of the best reasons to consider buying shares of PayPal. The company reported that total payment volume for Venmo soared 52% year over year in Q2. PayPal will likely expand the ways that it monetizes the P2P app, helping propel this popular stock to even greater heights.

3. Pfizer

Why is big, boring Pfizer (NYSE:PFE) so popular among Robinhood investors? Sure, the huge drugmaker hasn't delivered impressive growth in recent years, but Pfizer has two exciting potential catalysts on the way.

Pfizer and its partner BioNTech could be the first to win Emergency Use Authorization (EUA) from the U.S. Food and Drug Administration (FDA) for a COVID-19 vaccine. The two companies expect to announce preliminary results from a late-stage clinical study of BNT162b2 later this month. If those results are positive, the vaccine could realistically be on the U.S. market by the end of 2020. Pfizer and BioNTech already have a $1.95 billion deal with the U.S. government to supply 100 million doses of the vaccine pending EUA.

Another key upcoming potential catalyst for Pfizer is its planned merger of Upjohn with Mylan. The transaction is expected to close by the end of the year. This deal will boost Pfizer's growth by moving older drugs that are losing market share from its lineup to Viatris, the new entity formed by the merger. 

There's also another reason why Pfizer has been a popular stock with investors for a long time (well before Robinhood came on the scene) -- its dividend. Pfizer's dividend yield of over 4% is one of the most attractive in the healthcare sector. While the company's dividend will decline somewhat after the Upjohn-Mylan merger closes, investors who hang onto shares of both the "new" Pfizer and Viatris will still enjoy a similar combined payout.