Well I was tempted to go to BT Broadband and dump Sky...but after reading this I'm a lil wary
I was more than a bit wary going from O2 to BT Infinity but I've had a very good initial few months with zero problems so far.
At a cable run of around 500m from the cabinet we now have over five times the original download 'speed', which was a reasonably healthy 12Mbit with O2 and is now approaching 70Mbit/sec. The upload bandwidth increased by an even greater factor.
ETA: we're on the Ponteland exchange in North Umbria