Vodafone came bottom for dropped calls, with more than one in five made in rural areas failing to connect, according to data from the watchdog. Nationally, the network failed to complete an average of 7.4 per cent of all calls made.
EE topped the major networks, with three per cent of calls failing, which fell to 2.5 per cent in urban areas.
Ofcom also measured O2 and the Three network, which respectively dropped 4.7 per cent and 5.5 per cent of their calls nationally.
Vodafone said it "continues to invest in its network and services", adding it was spending £1 billion this year to improve coverage and quality.
The survey said O2 was best for urban calls, while EE was best for rural.
EE said: "We are investing hundreds of millions each year in expanding the reach of our network so more people can make calls in more places."
Across the country, one in 20 users said calls dropped unexpectedly every day, while 14 per cent of those in remote rural areas found they were unable to make calls.
The report defines remote rural areas as villages with populations between 500 and 2,000 more than 10 miles away from an urban area.
Some 78 per cent of people in urban areas were satisfied with their mobile network, compared to 67 per cent in rural parts of the UK and 70 per cent in remote areas.
The watchdog said the 3G networks of the four major networks covered about 90 per cent of the country.