Budget stores Aldi and Lidl have outperformed Marks & Spencer for the first time in an annual supermarket satisfaction report.
The Which? survey of more than 11,000 members placed Waitrose in the top spot for the third year running, receiving a score of 83% and praise for its staff and products.
The "big four" supermarkets - Tesco, Asda, Sainsbury's and Morrisons - failed to impress customers as much as budget alternatives Aldi and Lidl, which were ranked second and third respectively. Marks & Spencer came fourth.
Meanwhile Tesco and The Co-operative were given the joint lowest score of 46%. The former was awarded just two out of five stars on a range of subjects including customer service, own brand products and store environment.
Aldi and Lidl were both given four stars for the quality of their fresh produce and value. One Which? member commented: "I'm a new Aldi shopper and it's surpassed all expectation."
A spokesman for The Co-operative Food said: "Clearly we are disappointed by these results, but we are working hard to modernise the business and are investing heavily in improving all aspects of our offer, including product quality and availability.
"This is already paying off with our premium Truly Irresistible range scoring well."
A Tesco spokesman said: "We're disappointed and a little surprised by these results.
"They don't tally with our own measures of customer satisfaction or our experience in talking to some of the millions of people who shop in store and online with us every week.
"We want to keep our customers happy and invest hugely in doing so, by offering great value, providing excellent quality products and by constantly developing new products and services to meet changing customer demand."
Which? executive director Richard Lloyd said: "The tough economy and rising food prices have seen cash-strapped consumers heading to the discounters for their low prices and special offers.
"Aldi and Lidl have climbed to second and third place this year, overtaking Marks & Spencer. And this doesn't mean compromising on taste, as our tests show they sell a range of products that compete with the premium brands."
The Which? survey rankings are:
1. Waitrose 83%
2. Aldi 72%
3. Lidl 68%
4. Marks & Spencer 67%
5. Morrisons 60%
6. Sainsbury's 57%
7. Asda 51%
8. Tesco 46%
9. The Co-operative 46%