The top spot was claimed by JetBlue Airways, with a satisfaction score of 81 on a 100-point scale. Southwest scored 77, its lowest mark in five years.
The index has been tracking American consumer satisfaction since 1994. It is compiled after interviews with about 80,000 people on a range of products and services.
Increased passenger dissatisfaction with Southwest, which resulted in a four-point decline from last year, is most likely related to Southwest's merger with AirTran Airways and the associated disruptions as operations were consolidated, according to the index. Before this year, the Dallas-based carrier enjoyed an 18-year reign at No. 1.
By comparison, Delta Air Lines last year saw passenger satisfaction plummet after its acquisition of Northwest Airlines. This year, Delta's rating rose 16 percent to a score of 65 and its stock price increased 25 percent, the survey noted.
Southwest and AirTran account for about 70 percent of the passenger traffic at Baltimore-Washington International Thurgood Marshall Airport.
The satisfaction of leisure travelers was significantly higher than that of business fliers, 71 to 66 points. Overall, airlines improved slightly more than 3 percent from last year, to achieve a score of 67. The improvement means the industry stays a step ahead of the businesses rated lowest by the index: subscription television service (66) and newspapers (64).
The number of passengers surveyed who checked luggage declined 20 percent since last year. People who did not pay to check bags were happier than those who were assessed fees to do so, 73 to 62.