We have BT vision (bronze package) and I (and the kids) love it... however, having just looked online I'm shocked to learn I am paying about £20 a month more than I need to be for my complete BT package

(phonecall to bt tomorrow me thinks)!
Although you might lose some sky channels you may well find that the programmes are added to the "On Demand" section anyway (which I find very useful).
The service I have received from BT has been fantastic. I've had it for a couple years now and have never had any problems or interruptions. There was a bit of a cock up when I moved last year but it was easily resolved.