Take yer choice...Pipex, AOL, Freeserve, Zen, Force9, Tiscali, BT, Bulldog, etc., etc., they all use BT as a line provider and they are all reliable. It is unlikely that you will need the helpdesks more than once and there is always these forums for incisive help. The ISPs will all have those who have had problems (service, connection, billing) and those users who have had naff all problems (*ahem* moi) so any 'comparisons' are unlikely to be of much use.
For what it's worth I use Tiscali BB and have never had a problem with speed, service et al...however others could regard them as the evil impish servants o'de debble.
Connection quality is more to do with where you are based rather than the name of the ISP. When choosing I went for Tiscali because a). I used for for dialup since screaming.net days and found them brilliant and b). they offered a free modem, connection and filters. I was tempted with Pipex as they were slightly cheaper but better the devil ya know. Choose any of the above and take into account monthly cost, setup costs and period of contract. As all the connections go through BT you could do worse than signing up to the flute playing man.