Poor service, higher ticket prices and fees for checked bags are taking a toll on Americans who fly, and Delta Air Lines is bearing much of their dissatisfaction.

That's according to a widely-watched survey of customer satisfaction released Tuesday. Passengers gave airlines the lowest score among among all industries studied by The American Customer Satisfaction Index, which compiles scores on more than 225 companies in 47 industries. Passenger satisfaction with airlines dropped 1.5 percent to an ACSI score of 65 out of a possible 100, continuing a long slide. Delta posted the industry's worst score -- 56 -- down 10 percent.

One problem for airlines: business passengers, their most profitable market segment, are the least satisfied cohort. And because about 50 percent of fliers pay bag fees, dissatisfaction with the fees is worrisome.

Southwest, which just purchased AirTran Airways, led all airlines in passenger satisfaction, rising to a score of 81 to match its largest gap ever compared to the rest of the industry.

"Airline mergers typically have a destructive effect on passenger satisfaction," said Claes Fornell, who founded the survey at the University of Michigan.

Fornell said satisfaction with US Airways fell 8 percent in 2005 to an industry low following its merger with America West, and now Delta appears to be stumbling.

Delta said it has improved its on-time performance and completion rate, a measure of how many bags reach their correct destination on time. But those improvements in recent weeks did not show up in the survey because it was taken earlier in the year, the Atlanta-based airline said.

"Delta is focused on building a better experience for customers," said spokesman Eric Torbenson.

In contrast to air travel, dining out and visiting hotels are more enjoyable experiences overall for consumers this year, according to the survey. Wendy's, owned by Atlanta-based Wendy's/Arby's Group, topped the burger category. Intercontinental Hotels Group, which owns Holiday Inn, saw its score slip 3 percent to tie Best Western at 76.

Another Atlanta company posted a win, however. Sandy Springs-based UPS moved into the top spot among express delivery services, supplanting FedEx, which led the industry for more than a decade. UPS posted an 85, up 4 percent, as satisfaction with FedEx dipped 2 percent to 83.

"It's a very competitive industry," said David VanAmburg, managing director of ACSI LLC. "They both have to fight extremely hard. It's neck and neck. Very intense competition among a small number of players drives up [customer] satisfaction."

The survey was conducted in the first quarter of 2011. ACSI collected about 9,000 survey responses.