I reckon it's probably worth you having a good read on
http://www.adslguide.org.uk/ . It's pretty obvious that one ISP may be 10/10 for one area but for one reason or another they may appear to be shite somewhere else - I think on that site you should be able to work out who's good in your area. I've used BT for about 18 months and never had any problems whatsoever.