Although airline travel statistics abound, it may take a year to determine whether this year's grounding of Boeing's 737 Max aircraft models made much of an overall impact on the airline industry. According to the FAA's most recent installment of "Air Traffic by the Numbers," which is also called the ATO Fact Book, 2018 saw mixed results as far the growth of air travel. Here are some of the agency's findings, which were published earlier this month:

• The number of passengers flown by air carriers in 2018 increased by 4.8 percent, to 1 billion.
• The number of pilot certificates increased in 2018 by 3.9 percent, to 633,316.
• Flight delays fell in 2018 by 9%, to 260,325.
• Cancellations declined in 2018 by 3.4% to 101,303.

But these statistics fail to take into account the confidence that travelers may have in their airlines given the recent Boeing troubles, or the loss of business spurred by the international grounding of 737 Max models. What's more, there are a number of metrics both airline industry watchers and travelers take into account when determining which companies they like most, including mishandled baggage, flight delays and consumer reports. Wallethub recently took a stab at determining the best airline carriers in the U.S. in 2019. Researchers took into account the aforementioned issues along with in-flight comfort and relative travel costs. Its findings are outlined in the slideshow above, along with an additional metric from the U.S. Department of Transportation, which each month releases an "Air Travel Consumer Report." In general, the D.O.T. determined that just over 81% of U.S. flights run on-time. When they don't, the top reasons for delays are:

• Mechanical issues
• Security concerns
• Inclement weather

But Forbes recently reported that such challenges won't put much of a damper on travelers' summer plans this year. "This summer U.S. airlines are anticipating that a record 257.4 million of your closest friends will be joining you in the skies between June 1 and August 31, up 3.4% compared to a year ago," writes the magazine's Aerospace and Defense Contributor, Dan Reed. "And it means there'll be an average of about 2.8 million people flying per day during the summer. That's about 93,000 more per day, on average, over the summer of 2018." See also: 10 best airlines of 2018