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What's the most important thing to keep in mind when booking a flight? Aside from price, and how likely the airline is to lose your luggage, leg room and general seating comfort are tops.

If you're flying for more than five hours, you probably want more space to move around since deep vein thrombosis can be a huge concern. Space, however, can be hard to find as carriers try to squeeze in more and more rows to maximize passenger capacity per plane.

For our purposes, room is measured by “pitch,” the distance from a seat to the one behind it. Seat width and seat pitch can vary widely by airplane model and route.

The U.S.-based airlines on the following list have been compared based on data from sites like SeatGuruLifeHackerSeatExpert  and AirlineQuality.

JetBlue

JetBlue is often ranked very high in terms of leg room space. The pitch width of its economy class Airbus A320 is 34 inches. The pitch of the latest A321 is 33 inches and the seat width is 18 inches. Most fliers note that the “leg room is very comfortable.”

Southwest

southwest takeoff

A Southwest plane takes off in Dallas. The low-cost carrier has above-average pitch...but just hope you don't wind up in the last boarding group. (AP)

Southwest Airlines’ pitch is 32-33 inches on a long-haul economy flight with a Boeing 737-800. America’s largest low-cost carrier consistently boasts a 32-inch seat pitch on all seats except those on its Boeing 737-700 fleet, which offer a 31-inch seat pitch and a seat width of 17.3 inches, according to Cheapflights.com.

Virgin America

The pitch of the economy class Airbus A320 and A319 is 32 inches. The seat width is 19 inches. “I am very impressed the by seat comfort of Virgin America. Being 6/7 the seat legroom is of importance for me. It is some of the first planes and airlines, I did not touch the front seat with my knees,” one review read.

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Delta Air Lines

Delta Air Lines offers so many different types of routes and planes it’s hard to summarize the seat comfort in one pitch number. Most Airbus models vary between 31 and 32 inches. The different Boeing planes also have between 31 and 33 inches of leg room between seats, but some, like the Boeing 737-700, offer up to 36 in within certain rows

Allegiant

This American low-cost airline offers about 30 or 34 inches between seats. The seat width is 17 inches. One person wrote: “I am 6'0 and sat somewhat comfortable for 5 hours from Los Angeles to Hawaii. However, the seats do not recline, so you need to learn to sleep upright.”

American Airlines

American Airlines is another major American carrier with a lot of planes flying to hundreds of locations every day. Most aircrafts, whether Boeing or Airbus, have a pitch of 31-32 inches with a seat width between 17 and 18 inches.

Check out more of the Airlines Offering Least and Most Leg Room