If you get it Telewest Blueyonder Broadband is the best in my opinion - it might a cost a bit more than ADSL via a BT exchange but in return you get a quality, reliable and efficient service. They provide and maintain the modem, Ethernet is supported by default, there's no bandwidth capping and their customer service is just amazing.
If you can't then Plus.net are equally as good, especially when it comes to customer service; they do it the old fashioned way i.e. they actually try hard to keep their customers happy, rather than their stakeholders.
I haven't looked into the Talk Talk free BB offer but I'd be willing to be you get the free service in exchange of high
contention rate.
amofw