O2 outperformed its network rivals and independent retailers including Carphone Warehouse, which ranked below the industry average for a second year running.
JD Power's mobile retailer survey, which polled more than 2200 consumers, ranked retailers on their staff, stores and promotions.
Orange and Vodafone came equal last in the mobile phone networks category.
Phones4U topped the independent retailers category, ahead of The Link.
Despite enjoying record sales this year, Carphone Warehouse was still ranked below its rivals. A spokeswoman for the retailer said: 'This flies in the face of every customer survey and piece of research we have seen.'