Airlines least likely to require a 'Knee Defender'

Finding the best airline seats
Finding the best airline seats   

Whether you're looking to exercise your right to recline or hoping to avoid squashed knees, it pays to pick the right seat.

In recent weeks, passenger fights over reclining seats have diverted three flights—a Delta flight from New York to West Palm Beach, Florida, a United flight from Newark, New Jersey, to Denver, and an American flight from Miami to Paris. Paying up for extra legroom isn't a cure-all: In two of the three recent incidents, passengers were sitting in such premium seats.

Read MoreFight on board airliner boosts 'Knee Defender'

To avoid a tight squeeze—and avoid paying expensive additional charges for extra space—look to seat maps on sites such as SeatGuru.com or SeatExpert.com. Dimensions for basic economy seats can vary widely, and the difference in fares may be less than the fee to upgrade. (See chart of what U.S. carriers offer on short-haul flights, below.) "On JetBlue, even the seats that you don't pay for have more legroom than others," said George Hobica, founder of AirfareWatchdog.com.

U.S. airlines' seat dimensions on short-haul flights

Airline
Seat pitch
Seat width
AirTran 30-31" 18"
Alaska Airlines 31-32" 17"
Allegiant 30" 17-17.5"
American 30-32" 17.2-18.5"
Delta 30-33" 17.2-18.25"
Frontier 30-31" 17-18"
Hawaiian Airlines 30-32" 17-18"
JetBlue 30-34" 17-18.25"
Southwest 31-33" 17"
Spirit 28" 17.75"
Sun Country 31-33" 17"
United 30-32" 17-20.5"
US Airways 30-32" 17-18.25"
Virgin America 32" 17.7"
SOURCE: SeatGuru.com

Sites will also warn you off seats that have space constraints, like those ahead of exit rows that won't fully recline, or that are a little narrower because the tray table is in the armrest.

If all that's left at booking is the dreaded middle seat, check back periodically to see if a better seat has opened up, Hobica said. Aisle seats often do, especially in the day or two before departure, as elite frequent fliers are offered upgrades or decide to use miles for them. "Usually the people who are upgraded have the better seats anyway," he said.

And if you are willing to pay for an upgrade? Price that in at the start, to better compare comfort and price. "People hate Spirit, but seriously, their Big Front Seat product is still cheaper than many airlines' economy seats," Hobica said. But don't necessarily grab the upgrade at booking. SeatGuru.com reports that premium economy prices can be significantly cheaper booked closer to departure—although you do risk missing out altogether.

—By CNBC's Kelli B. Grant