I have been with TT for many years. Their support is not too bad (I try to use online chat if possible).
I have Fibre-to-the-cabinet now and am pleased with the speeds. Reliability is 99% and I use it pretty much 18 hours a day working from home.
I have had a few performance issues with the standard router they provided (they did send me another of the same type for free) but had to buy a more expensive one in the end - but maybe their new router is better?
The other issues I had were actually OpenReach issues rather than TT issues (wires/exchange).
TT's rates are competitive, unlimited broadband and I get free £5 mobile contract thrown in too. Unlike BT or Sky, they don't hike the price after 12-18 months and then every 6 months thereafter!