Price is always a big consideration when booking a flight, but frequent travelers also consider which airline is offering that price. Those passengers are aware that they may be stuck on a plane run by an airline company that doesn't provide good service.  

A recent report released the rankings of airlines, and Virgin America came out on top, as the airline that did the best job for its customers among leading U.S. airlines last year.

In addition to ranking at the top overall, Virgin America, which is headquartered in Burlingame, California, also had the best ranking related to baggage handling and the second-lowest rate of passengers denied seats from overbooking.

United Airlines, received the worst overall ranking.  Last year, their consumer complaint rate nearly doubled. United recently merged with Continental Airlines, and there have been difficulties in the integration of operations for the two carriers.

United's 2012 ranking doesn't reflect its experience over the past six months, in which the airline has made significant improvements in service, said company spokesman Rahsaan Johnson.

"Customer satisfaction is up, complaints are down dramatically and we are improving our customers experience," he said in an e-mail to the Associated Press.

This report came out after airline carriers overall had their second best performance in the more than two decades since research began measuring quality of service.

The report ranked the 14 largest U.S. airlines, using factors that include on-time arrivals, mishandled bags, consumer complaints and passengers who bought tickets but were turned away because flights were over booked.

The number of consumer complaints filed with the Department of Transportation overall increased by one-fifth last year, reaching 11,445 complaints, up from 9,414 in 2011.

"Over the 20-some year history we've looked at it, this is still the best time of airline performance we've ever seen," said Dean Headley, a business professor at Wichita State University in Kansas, a co-author of the report.

The best year was 2011, which was only slightly better than last year.

This doesn't mean airlines still do have problem areas to address. Carriers keep shrinking the size of seats to fit more people on planes, and empty middle seats that used to provide a little more room are no longer. More people who have purchased tickets are being turned away due to overbooking.

It's not surprising that passengers are getting grumpier, Headley said.

"The way airlines have taken 130-seat airplanes and expanded them to 150 seats to squeeze out more revenue, I think, is finally catching up with them," he said. "People are saying, 'Look, I don't fit here. Do something about this.'

"At some point airlines can't keep shrinking seats to put more people into the same tube," he said.

Airlines are now looking to decrease the size of the already compact bathrooms in order to possibly squeeze more seats on the plane.

"I can't imagine the uproar that making toilets smaller might generate," Headley said, especially considering the weight problem plaguing the country. 

"Will it keep them from flying?" he asked. "I doubt it would."

Regional carrier SkyWest has the highest involuntary denied boarding rate last year, while both JetBlue and Virgin America were industry leaders in avoiding the practice, with rates of 0.01 and 0.07.

Consumer complaints were also significantly higher in June, July and August, when planes are the most crowded.

"As airplanes get fuller, complaints get higher because people just don't like to be sardines," said Robert W. Mann, Jr., an airline industry analyst.

These complaints are regarded as indicative of a larger problem, because airline passengers may not be aware that they can file complaints with the Transportation Department, which regulates airlines.

The report's ratings are based on statistics kept by the department for airlines that carry at least one percent of the passengers who flew domestically last year.