In this segment from MarketFoolery, host Mac Greer and Motley Fool senior analyst Matt Argersinger check in with the world's biggest airline operator, United Continental (NASDAQ:UAL), which reported on a surprisingly good second quarter this week.

All the metrics under its control were going in the right direction, and the one key number it can't steer -- fuel costs -- didn't drag on the bottom line to the degree many watchers had feared. The duo consider what this quarter's results say about the industry, and Matt picks his favorite airline stock to buy now.

A full transcript follows the video.

This video was recorded on July 18, 2018.

Mac Greer: United Airlines reporting better than expected second quarter profits. Matt, you look at the numbers here, pretty impressive. Average fares, rising. Traffic, rising. Fuel cost, rising also, we'll talk about that. United went on to increase its profit forecast for 2018. Shares up around 6% at the time of our taping.

Matt Argersinger: Nice day for United Continental. If you look at the key unit metric, which is revenue per available seat mile, up 3%. Following the industry, that's a really strong number for this particular quarter. They also guided for 4-6% growth in that number for the next quarter. I've seen similar announcements from Delta saying the second half of the year is going to be stronger and stronger. It seems like this higher capacity is actually meeting higher demand, which is great for the airlines.

You mentioned fuel prices. Fuel prices are up 40% roughly year over year. Delta came out last week and slashed their earnings estimate for the year because of the higher fuel prices. I think a lot of investors thought United would be saying the same thing today, but they're not. Fuel prices are a factor, but they've been able to surpass a lot of that by controlling costs in other parts of business. And, as we were talking about before the show, all the other ways that airlines can pull revenue these days. Some of it feels like nickel-and-diming to us travelers, but I'll tell you what, they've become ingrained. We're so used to paying for luggage, paying more for slight upgrades in seats. We're talking two inches of additional legroom, and we're going to shell out $90 or something like that.

All these things that the airlines didn't have before have increased their pricing power. It's an industry that I think has certainly changed for the better.

Greer: Let's talk about the stocks. When we look at the five-year chart, first of all, we have the S&P, over the last five years, up around 84%. Looking at some of the big airlines, Southwest up a little more than 300%. That's the leader in the pack. This is over the last five years. JetBlue up 190%. Delta 175%. United 115%. American 110%. So, a double over the last five years. When you look at those stocks, do you have one going forward that you think is best in breed?

Argersinger: I've been talking about it a little bit on our radio show, Delta to me is the one. If you're an investor, I think you can buy a basket and do well. Even though the results over the last five years have been great, I think the next five years could be just as great, if not better.

But, Delta is my pick. Having studied it, I see what I think is the strongest hub and route network. They have the lowest unionized workforce. Only roughly 17% of their labor force is unionized because they only allow their pilots to union, which is unique in the industry. They have the only investment-grade balance sheet, and that's a product of generating lots of cash, paying down debt, paying down their pension liability. They bought back 15% of their shares over the last five years. They have a new $5 billion buyback plan in place, they pay a 2.5% dividend yield.

All of that is good for about 10X earnings. So, I'm not saying you could buy Delta or airlines today and expect it to double or triple in the next five years. But another double in a reasonable amount of time that beats the market? I think you have it.