Do you live in a cable area? I've been with Telewest (now Virgin Media) for years and service has been nothing short of excellent. The main advantage you will find with cable over all other ISPs is that you are not affected by how far away you are from the exchange, the line quality or the contention ratio. Also if you do have a problem they cannot send you on a run-around by passing the blame onto BT who would then normally pass the blame back to the ISP!
The cable companies are known for rolling out speed upgrades on a fairly regular basis and I would expect another one in the not too distant future.