It was awarded 67 out of a potential 100, under a system that gave scores of 0-5 in 20 best-practice criteria.
British Airways came second with 65% and Travelbag third with 62%.
On average, airline sites fared worse than online travel agents, with the former scoring just 48% usability and the latter 55%.
Monarch and Ryanair scored lowest with 38% and 40% respectively. They were among several airlines criticised for not being transparent with pricing and not giving enough detail about exactly where the airports they served were located.
Webcredible director Ismail Ismail said: 'It’s not acceptable to add ‘hidden’ charges at the very end of a transaction process. This is something which a number of airline carriers are guilty of.’
He added that many of the sites also suffered from 'inaccessible user information'; 15 out of the 20 scored 0 out of 5 for provision of information, with details of airport locations and transfers to city centres lacking in many cases.
Ismail also said failure to embrace Web 2.0 technologies was an issue. For example, many sites did not even provide users with such rudimentary sharing tool features as the option to ‘email a friend’.
See also:
ABTA urges OFT action on Ryanair (28/02/08)
Opodo achieves first ever profit (30/01/08)
Internet shoppers increase by 40% worldwide (28/01/08)
US survey shows satisfaction levels falling (28/11/07)