According to the study, BT, Sky, TalkTalk and Virgin Media between them occupy the bottom of the Which? league table.
Sky and TalkTalk did particularly poorly, earning the lowest rankings overall.
However, Which? is withholding the names of the best performing operators for its paying subscribers.
TalkTalk, which has a reputation for cheap deals, was criticised for the quality of its customer service and tech support. Customers said that their connection dropped out frequently.
Sky subscribers also complained on slow speeds with two-thirds saying they were likely to switch to another provider.
One in five BT customers criticised the telco for very slow speeds or connection dropouts.
Virgin Media performed slightly better, but was criticised for its price increases, more than half said the price of their deal had risen in the past 12 months.