The stock market started 2021 with a bang, but those early gains evaporated in February. When Fools love it when stocks decline, because it gives us a chance to buy our favorite businesses at discounted prices.

What stocks do we think are top opportunities today? We asked five Motley Fool contributors to weigh in, and they called out SL Green Realty (SLG -2.18%) (PRTS 10.00%), Etsy (ETSY 3.38%), Etsy (ETSY 3.38%), Uber (UBER -0.13%), and Airbnb (ABNB 1.14%).

A hidden e-commerce winner

Jeremy Bowman ( 2020 was a great year for e-commerce stocks thanks to the pandemic, and was among the big winners, with shares up nearly 500%. Even with the economic reopening coming up, however, 2021 looks set to be another strong year for the auto parts retailer.

First, the opportunity is more than just an e-commerce play. The company's in the midst of a turnaround that began in 2019 when new management took over. Under CEO Lev Peker, has jettisoned underperforming brands and consolidated the company's operations, which had previously included banners like JC Whitney and Auto Parts Warehouse, under the brand, making marketing and brand-building much more efficient. It also changed the corporate name from U.S. Auto Parts to The turnaround initiatives, which also include opening new distribution centers and upgrading its tech infrastructure, are delivering results. Gross margin has increased for six quarters in a row now, allowing the company to reinvest a greater percentage of revenue back in the business, and e-commerce sales jumped 105% in the third quarter.

A number of macro factors are supporting the company as well. Auto parts sales are traditionally strong coming out of recessions as consumers delay buying new cars, and the spike in used car sales during the pandemic should favor auto parts sales as will the increase in vehicle miles once the economy reopens. will report fourth-quarter earnings on March 8. Currently, Wall Street only sees the company's revenue growing 12% this year, which looks like a lowball estimate. If that's the case, the stock should have a lot of upside from here.

About to get a big shot in the arm

Matt DiLallo (SL Green Realty): Last year was a tough one for Manhattan's largest office landlord, SL Green Realty. The pandemic greatly affected New York City, keeping office tenants out of their Manhattan skyrises.

However, office buildings are about to get a shot in the arm as vaccines roll out, allowing people to start occupying them again. While companies quickly pivoted to remote work, most can't wait to return to their offices because they're vital for productivity, mentoring, and creating culture. That's why SL Green was able to collect 97.9% of the office rent it billed last year and sign more than 1.2 million square feet of new and renewal office leases even though most offices remained unoccupied.

Because of that eventual return, the value of high-quality office properties has held up relatively well. That allowed SL Green to take advantage of the market to sell several properties over the past year at excellent values. Those sales gave it the cash to shore up its balance sheet, pay a special dividend, and buy back its beaten-down stock, which tumbled by more than 25% since the start of 2020. The REIT was also able to increase its monthly dividend for the 10th straight year, pushing the yield above 5%.

Shares of SL Green could soar like a Manhattan skyscraper this year as companies get the "all clear" to return to their offices. Add that to its generous income stream, and this REIT looks like a winner.

An Amazon-proof e-commerce winner

Brian Feroldi (Etsy): When it comes to e-commerce, (AMZN 1.60%) tends to suck all the air out of the room. However, the shift from offline sales to online sales is so massive that lots of companies are poised to win.

Etsy has clearly established itself as one of those e-commerce winners. The company's platform connects buyers and sellers of homemade goods, which is a growing niche that insulates it from the other e-commerce competition. 

Etsy's 2020 numbers show that demand for the platform is soaring. The company ended the year with 4.4 million active sellers (up 62%) and 81.9 million active buyers (up 77%). Total spending on the site more than doubled to $10.3 billion.

Etsy took full advantage of the surging demand. Revenue grew 111% to $1.7 billion. The top-line growth was so strong that Ety's net income grew 265% to $349 million even though it significantly increased its spending on marketing, product development, and hiring.

Management doesn't think the hypergrowth is ending anytime soon. Revenue is expected to grow at least 125% in the first quarter of 2020, and margin is expected to remain strong for the foreseeable future.

All of this goodness has pushed Etsy's stock to a well-deserved all-time high. With shares are trading around 100 times 2021 earnings estimates, investors have to pay up to buy the stock right now. However, great companies usually trade at a premium, and Etsy's results prove that it is a great company. I think the outperformance is here to stay.

Take a ride on this stock

Adam Levy (Uber): Uber is well positioned to capitalize on the return to travel and reopening the economy. The company has the unique ability to leverage its two-sided network of drivers and customers into new (and old) opportunities across its range of services. Other singularly focused "gig-economy" companies don't have this capability.

Uber's most valuable assets are its local networks of drivers and customers. Over the last couple of years, management took steps to exit markets where its network wasn't big enough to provide a competitive advantage. It also sold off several non-core assets. As a result, Uber enters 2021 a more focused company with a stronger network advantage.

That advantage will come in handy as people return to travel. Most notably, the delivery business ought to act as a tailwind for the more profitable mobility business, as Uber makes it easier for customers and drivers to switch between services. The company has already seen the benefits as management says the ride-hailing business has come back faster than other forms of transportation.

Despite the massive downturn in mobility revenue last year, the segment remained profitable on an adjusted EBITDA basis. The reopening will cause growth in Eats to slow, but improving take rates and operating leverage should bring it toward positive EBITDA. As a result, management expects the company as a whole will produce positive EBITDA in 2021, as the delivery business sees improved profitability and mobility bounces back. 

Open the door to this travel stock

Chris Neiger (Airbnb): Some investors may balk at the idea of investing in the home-sharing company while we're still in the midst of a pandemic, but there are two reasons that won't matter soon. First, the pandemic will end and travel will return. Second, Airbnb is perfectly positioned to benefit when it does. 

Travel certainly took a hit over the past year, and Airbnb's revenue fell along with it. The company's sales dropped 22% in the fourth quarter. But you have to put that drop into context. Consider that the company's fourth-quarter revenue of $859 million blew past analysts' consensus estimate of $748 million. And for the full year 2020, revenue was down just 30% compared to 2019 -- during a time when essentially the entire world wasn't traveling. 

With many parts of the U.S. opening back up and coronavirus vaccines being distributed, Airbnb is optimistic that there will be "a significant travel rebound" this year. 

And then there's Airbnb's position in the travel space. Airbnb is already a clear leader in the home-sharing market and once more people feel comfortable traveling again there's no reason why bookings won't spike for the company. Airbnb offers unique experiences and rentals that can't be found anywhere else and you can bet that people who've been cooped at home for the past year are itching for both. 

Maybe I'm biased toward Airbnb because I used the service to take a four-month-long road trip with my family in 2019, but I'm not the only one that's been impressed with the company's business. Investors have pushed up the company's stock more than 40% since it went public back in December.

Those investors are focusing on Airbnb's $3.4 trillion total addressable market opportunity and understand that the company offers rentals and experiences that its competitors can't match. For investors looking for a unique company that's likely to see huge growth as travel rebounds, Airbnb looks like a great pick.