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The no-frills airline, which faced enforcement action from the Civil Aviation Authority after failing to properly inform people of their rights following the cancellation of thousands of flights earlier this year, came in joint last place with Vueling with a customer score of just 45%, scoring just one star from flyers for seat comfort.
British Airways also scored low and slumped to third from bottom of the table, achieving a customer score of just 52%. It was ranked mid-table the previous year, with a customer score of 67%.
In a year when BA did away with free food on most short-haul flights and instead introduced paid-for M&S sandwiches, passengers gave the airline's food and drink just two stars. The same poor rating was given for seat comfort and value for money when flying short-haul.
Meanwhile, Jet2.com (76%) and Norwegian (76%) ranked high and are proof that cheap prices don't have to mean poor service. Both budget carriers were awarded four stars by passengers for their customer service.
The top spot went to Aurigny Air Services (80%), with the Channel Islands carrier gaining four stars from passengers for its boarding process, cabin environment and customer service.
Rory Boland, Which? Travel editor, said: "Passengers are telling us that there are many different ways to be a great airline, but providing great service at an acceptable price is a must have.
"BA's poor customer satisfaction shows it clearly needs to step up its game in a year that has been beset with problems. From the food and drink on offer, to the poor value for money of the journey itself, the airline has a lot of work to do to improve the experience that passengers associate with the airline."