I switched broadband from sky to virgin, best thing I ever did.
On sky I used to get 6mbps, then it dropped to 3, then to 0.01mbps!!
Sky told me that there was no fault and that was the best I could get on my phone line. 0.01mbps they were taking the piss!
On virgin we pay £33.50 for broadband only, no phone line required, we've all got mobiles with unlimited calls so don't really need one.
The slowest I've had on virgin is 30mbps, the highest 115mbps, usually averages out at between 70-80mbps.
Definitely worth switching, cost us a about fiver more on virgin than sky.