Which? survey reveals customers' least favourite mobile network
Vodafone has been rated as the UK's worst mobile network provider for the eighth year in a row, in consumer lobby group Which?'s eighth annual survey.
EE and O2 also finished in the bottom three. Virtual network provider Giffgaff came top of the poll, ahead of Utility Warehouse and Plusnet Mobile.
Which? said the study proved that good "customer service" and "value for money" were important to people.
Vodafone said it was "sorry" that Which? members were unhappy with them.
In a statement, the company added: "We are working hard to understand the issue and what more we can do."
In all, 13 networks were included in the survey of 6,135 Which? members in February.
The survey said Vodafone had collected one-star ratings for customer service, value for money and technical support.
One in five of its customers told Which? that "customer service, including complaints handling and the way their queries were dealt with, was poor".
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Only 27% of EE customers said they had received good or excellent service for technical support, while one in 10 O2 customers rated the value for money they received as "poor".
An EE spokeswoman said: "We're ranked top by OpenSignal for mobile experience in the UK, which is supported by other independent reports from Ofcom and RootMetrics.
"Ofcom's latest figures also show that EE receives among the fewest complaints in the mobile industry, as we've continued to invest in the UK's best customer service."
Nearly all Giffgaff customers said it was "good or excellent" for value for money, adding they would recommend it to friends and family.
Sim-only deals proved on average 31% (£3.56 a month) more expensive with the Big Four providers (EE, O2, Vodafone and Three).
The same was true for the average monthly contract price for an iPhone XS, which was 18% more (£10.11) with the Big Four, while a Samsung Galaxy S10 was 6% more expensive (£3.22).
Natalie Hitchins, Which? head of home products and services, said: "The continuing reign of smaller networks over the big players goes to show exactly how important customer support and value for money are to mobile users.
"If you think you're paying too much or are not getting the level of service you expect from your provider, you should shop around for a better deal - you might find you save yourself some money and probably a lot of grief, too."