At the bottom of the list compiled by price comparison and switching website uSwitch.com were BT and ntl. It was a second poor performance from the two companies, who also finished bottom of a home phone customer satisfaction study.
Connection quality was found to be the factor most important to broadband customers.
Overall levels of ISP satisfaction were found to be high in the UK.
Chris Williams, broadband product manager at uSwitch.com, said: "Less encouraging is that once again, as with the results of our home phone survey, it is the companies with the largest numbers of customers who are failing to meet their customers' expectations.
"The broadband market is constantly evolving, and before the end of the year we can expect to see connection speeds increase further and prices continue to fall."
He added: "This should provide an incentive for all broadband users to review their current package at some point during the next 6-12 months and make sure that they are getting the best deal all round."