Well I was tempted to go to BT Broadband and dump Sky...but after reading this I'm a lil wary
It's pot luck really - there is far more variability within each ISP than between them. Never EVER go by the experiences of a handful of people posting on an internet forum (not even my 4 month Sky debacle I mentioned above).
The one thing I'll say is that once you've had a bad experience with one ISP, it makes you feel a hell of a lot better to dump them and move to another. In fact, that's the very best way for us the great British public to collectively kick them up the backside. It's also likely that you won't suffer similar problems with the new provider (whoever it is) unless you know there's a particular infrastructure problem in a particular area (long lines, for example)..