Can only echo the above, re BT ADSL.
We've had it in here for about a year now, and it has given faultless, fast service. Service speed (average) is about 450kbps downstream and 200kbps upstream.
Many of our friends around here (Edinburgh) use Telewest (BlueYonder [cable DSL]) and have reported similar trouble-free service.
One thing to point out, however, is that many of the speed difficulties you find on the internet are actually the server at the other end - not your connection. Can be very frustrating sometimes!