TalkTalk and BT have received the worst customer satisfaction scores in a survey of 12 broadband providers.
They scored 38% and 45% respectively with their customers, while Sky (48%) and EE (49%) came close behind them in the Which? survey of 1,800 people.
Frequent price rises, connections that drop, unreliable speeds and "woeful" customer service all contributed to the scores, the consumer group said.
The four account for almost three-quarters of the UK broadband market.
BT alone accounts for almost a third of the country's broadband connections.
Zen Internet had the highest customer rating at 86% in the survey, followed by Utility Warehouse (81%), John Lewis Broadband (68%), SSE (66%) and Plusnet (65%)
Virgin Media (52%), Vodafone (50%) and the Post Office (48%) were also included.
Which? surveyed people about their broadband in November and December. The customer score is based on satisfaction levels with their provider and whether they would recommend it to others.
Those surveyed were also asked to evaluate aspects of the service, with five stars being the highest rating in seven categories, including speed, reliability and customer service.
BT scored just two stars in all seven categories, while TalkTalk also scored two stars in each except value for money, for which it got three stars.
Just four of the 12 providers scored more than three stars for speed: Zen Internet, Utility Warehouse, Virgin Media and Vodafone.
'Long way to go'
Alex Neill, Which? managing director of home services, said: "The big players still have a long way to go to satisfy their customers, so if you're unhappy with your broadband, complain and look to switch if your service doesn't improve."
A BT spokesperson said it was disappointed with the survey result and apologised to any customers who had been let down.
"Generally, our broadband performs extremely well for customers and offers very reliable speeds at peak times, according to the latest Ofcom broadband speeds report."
A TalkTalk spokesperson said: "Our extensive improvement programme has already led to fewer faults, faster average speeds, shorter times to resolve issues and customers reporting higher satisfaction levels."
Ofcom, the telecoms regulator, said last month that broadband customers who suffered poor service may get automatic refunds under new plans.
Its own survey suggested that 51% of broadband customers were "very satisfied" with their provider, with 36% fairly satisfied.
That meant a "significant" minority - 13% - experienced poor service, mostly due to slow speeds or loss of service, it said.
BT had the lowest score for "very satisfied" of the four providers in the Ofcom survey at 45%, followed by TalkTalk on 49%, Sky on 52% and Virgin Media on 55%.
Last month BT agreed to Ofcom demands to legally separate Openreach, which runs the UK's broadband network, in a bid to give better service to both consumers and broadband providers.
Digital minister Matt Hancock said: "Too many people are suffering from poor customer service when things go wrong with their broadband.
"Getting a better deal for consumers is at the heart of our Digital Economy Bill, which strengthens Ofcom's power to make sure providers pay automatic compensation when service falls short."