What happened The so-called "reopening trade" gained velocity in early 2021, and airline stocks were among the beneficiaries. Southwest Airlines (NYSE: LUV) gained 13.9% in the first six months of the year, according to data provided by S&P Global Market Intelligence, and was up as much as 36% in April before falling back some. LUV data by YCharts So what Airlines were among the industries hardest hit in 2020 by the pandemic, with travel demand all but evaporating a year ago. As the vaccine rollout picked up pace so did demand, and some of the sectors that were hardest hit at the height of the pandemic posted impressive gains starting last fall and heading into this spring. The airlines were among them. Southwest's mid-spring 36% gain for the year actually trailed a lot of other airlines including American Airlines Group (NASDAQ: AAL), JetBlue Airways (NASDAQ: JBLU), and Hawaiian Holdings (NASDAQ: HA). One thing all of those airlines have in common is they are all aggressively chasing leisure business. Image source: Southwest Airlines. With tourists, and not businesses, leading the way back to the airports, the airlines that have route networks and ticketing policies favored by leisure travelers have seen the recovery materialize faster than rivals who rely on corporate accounts. The rally fizzled in recent months amid concerns about new variants, and based on suggestions from analysts that the stocks have begun to get ahead of the businesses. Now what It's an odd moment right now for airline investors, and in particular holders of Southwest. On one hand, the airlines are definitely off the lows from the pandemic. Southwest remains a best-in-class operator with a strong balance sheet and the wherewithal to ride out whatever potential turbulence lies up ahead. On the other hand, the company's longtime CEO Gary Kelly is preparing to step down, and the airline is having a miserable summer when it comes to staffing its flights and avoiding cancellations. There's nothing wrong with holding Southwest for the long haul and riding out the current storms, but I'd advise caution to those considering buying in right now. Until Southwest's internal issues are behind it and we are sure the pandemic is fully under control, there is likely a ceiling on how high the airlines can fly, and after the first half rally there might not be much more room to run for now. 10 stocks we like better than Southwest AirlinesWhen 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 Southwest Airlines 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 Lou Whiteman has no position in any of the stocks mentioned. The Motley Fool recommends Hawaiian Holdings, JetBlue Airways, and Southwest Airlines. The Motley Fool has a disclosure policy.Source