What Which? are you reading?
Opens this months Which? (Oct 2017) to page 42 "TV & Broadband Providers"...
TalkTalk are mid-table with "customer score" of 51% (behind PlusNet & EE, ahead of BT & Sky, neck & next with Virgin but rated higher overall).
Maybe they've also done another survey, but as this is out in the same months magazine, and it's a 4 page article, is it perhaps worth mentioning?
[ Disclaimer - single anecdote is not authoritative but ~10 years with TalkTalk, esp. on Fibre, much happier with TT than other ISPs when I had a troublesome physical line which was really OpenReach's problem. IMHO TT get a lot of the "cheap end" of customers who are less able to understand the physical limits of ADSL. If you're a long way from the exchange you won't get a magical data rate from any ISP. And this is the source of quite a number (not all) of complaints. The user forums frequented by their UK based tech staff are very helpful and let me mostly bypass phone support ].