Sky broadband isn't particularly well-rated in most reviews.
If you're prepared to pay a fairly high price for excellent quality, Claranet is possibly the best ISP. (Claranet provides mainly business services, with many major companies using it. It regularly comes out as the best ISP in independent reviews of business providers. The same service is available to home users but it's far from cheap):
http://www.claranet.c...me-broadband-services
Independent reviews of the 'big boys' providing home broadband services usually put BT at the top of the table. (Again, it's certainly not the cheapest option available):
http://www.productsan...oryId=CON-TOTAL-BB-R1
Among budget providers, BE Broadband is usually well-rated. (Nearly all home services 'throttle' download speeds at certain times, or for certain types of traffic. BE Broadband is the only ISP which guarantees never to do so):
http://www.bethere.co.uk/
Chris