EE registered the most broadband complaints, as a proportion of its customer base, during the final three months of 2014.
The broadband provider - which BT will acquire for £12.5 billion, subject to regulatory approval - received 0.42 complaints per 1,000 customers between October and December.
This compared to 0.26 for BT, 0.23 for TalkTalk, 0.22 for Plusnet and 00.6 for Virgin Media and Sky - the two best performers during the final quarter.
Ofcom's research shows the average broadband provider registered a score of 0.16 during the final quarter of the year.
According to the study, EE has been the worst performer in terms of customer service for the last four quarters, meaning the latest result comes as little surprise.
The firm witnessed 0.33 complaints per 1,000 customers in Q3 2014, 0.34 in Q2 2014 and 0.42 in Q1 2014.
Not since BT registered a score of 0.32, compared to EE's 0.29, in Q4 2013 has another broadband provider fared worse in the Ofcom study.
In the final three months of 2014, EE received complaints relating to faults, service and provision problems, complaints handling and switching issues.
Claudio Pollack, Director of Ofcom’s Content and Consumer Group, said the regulator's figures help inform consumers' choices of telecoms services.
"There are now more providers included in our report, so people can compare complaints figures for all the biggest companies," he stated.
"While operators still have room to improve their performance, it’s encouraging to see a continuing decline in the total volume of complaints."