BTs service is average to say the least and we used to get cut off all the time.
We switched to Sky as we were already using their TV service and it costs us an extra �10 a month which is for unlimited downloads and upto 16MB, we get around 10MB at the moment. That is their top package, the other two are �5 a month and free.
If you already have their TV, then definitely consider their broadband, you don't have to switch your line rental like a lot of other providers force you to do - Orange are guilty of this and will also tie you into an 18 month contract.
If you don't have Sky and don't want to switch your line rental, then you might as well go with BT, although the Home Hub thing they foist on you is useless, so if you have another router you can use I'd stick with that.
If switching your line rental doesn't bother you, then Virgin came top in a recent survey and the speed is good especially if you live in one of their cabled areas which is about half the UKs population