A survey of more than 10,000 online Christmas shoppers has revealed that Amazon's US and UK websites rank the highest for customer satisfaction.
With a customer satisfaction score of 83%, Amazon UK beat Play.com (81%) and John Lewis (78%), according to research by Foresee.
The most improved UK websites were Marks and Spencer, which raised customer satisfaction by 5% on last year to 78%, to enter the top five retailers.
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Littlewoods.com also showed a 5% improvement from 2009, to 71%.
Larry Freed, CEO at Foresee, said, US websites are outperforming UK websites.
"The largest retailers often have significant dedicated resources to improve the online customer experience, even during a global recession.
"Despite powerful evidence pointing to the positive impact of a top-notch customer experience, many companies have not made these experiences a priority," he said.
Some of the lowest-scoring UK websites included RyanAir, Ticketmaster and Very.co.uk.
Dell EMEA declined 3% on last year's figures to score a rating of 68%.
Foresee warned that retailers scoring below 72% are risking customer loyalty, sales and market share and need to improve website functionality.
Amazon was the clear leader last year, with a customer satisfaction score of 83%. In 2008, it was equal top with Play.com, scoring 78% for customer satisfaction.
Foresee surveyed over 10,000 online shoppers during December to create its Christmas customer satisfaction index across the UK's top 40 online retail websites.