The 23rd annual Air Quality Rating (AQR) has released its evaluation on the performance of the 14 largest U.S. carriers in 2012 based on data from the U.S. Department of Transportation.

Virgin America topped the list. According to the researchers, 2012 turned out to be the second best year for the airline industry in 23 years they have been ranking the carriers. 2011 has been the best year for the airline industry.

Virgin America logo

The research was conducted by Omaha, Nebraska-based Wichita State University and Purdue University in Indiana. Carriers were ranked on the basis of consumer complaints, mishandled bags, on-time arrivals and denied tickets. Burlingame, California-based Virgin America had the best baggage handling rate (0.87 bags mishandled per 1000 passengers), while American Eagle was worst in this category with 5.80 mishandled bags per 1000 passengers.

United Airline was the worst performer in 2012. The company merged with Continental Airlines, but the two companies have had a rough time integrating their operations. Consumer complaints at United Airlines almost doubled to 4.24 complaints per 100,000 passengers in 2012. Overall, the consumer complaints were up about 20 percent from 9,414 in 2011 to 11,445 last year.

Dean Headley, a Wichita State University professor who co-wrote the annual report, said that the airline performance has increased in the past few years, but passengers increasingly getting more grumpy. Airline carriers have been shrinking the size of seats to accommodate more people into planes.

Today more people are being denied seats because flights are overbooked. In fact, many carriers are planning to reduce the size of toilets to squeeze in a few more seats, according to TimeHeadley believes that making toilets more compact would create an uproar, but that won’t keep them from flying.

The rate of consumer complaints per 100,000 passengers increased from 1.19 in 2011 to 1.43 in 2012. Earlier, when there were overbookings, carriers would find passengers who would give up their seat for cash, a free ticket for another flight later that day or the next morning. However, now there are no seats available on next flights, so people are reluctant leave their seats. JetBlue was  on top in avoiding denied bookings.

Talking about the on-time arrival, Hawaiian Airlines was the top with 93.4 percent flights on time in 2012, while American Airlines and ExpressJet were the worst performers as only 76.9 percent of their flights were on  time.

Overall, the on-time performance has improved in the past few years as carriers cut back on the number of flights.