Depends what you want. TV, telephone and broadband all in one? Or just broadband and phone. Or just broadband.
I am going through the transition phase of changing my provider ORANGE. So I have been doing lots of digging.

There are 2 technology you should be aware of ADSL2+ Twice as fast as normal. Doubles the capacity.The other one FIBRE broadband which says it will give 100MB in future. This is provided by Virgin at the moment.
I have found Orange to be slow and disconnect too much. It is alright for a beginner I guess.

There are many things to take into account like distance from exchange, length of cables, wireless security, router firmware.

It is not what I require since I have Xbox360, I require fast connection for the games.

I hope this website helps http://www.broadbandwatchdog.co.uk/b...-providers.php

Good hunting. Let me know how you pick. I am thinking on SKY.