The reality seems to be that they all start OK and go downhill. I'm on my third ADSL ISP. I changed each time when it got to the point that the helpdesk hadn't a clue. Each time I ended up talking to extremely polite Indians, reading from a script that didn't address the problem I had, and unable to depart from the script.
While blackace comments that the site I pointed out last year isn't independent, the outfit that he says sponsors it does come half way down the ratings. I chose UKFSN for my Essex home, based on that site, and have not regretted it for a minute.
If you look at where Tiscali comes on the ratings (all from users), you'll see it seems consistent.
PlusNet had problems, but to give them credit, they tackled those problems and the experience I've had over the past year in Norfolk has been excellent.