I've currently got Sky fibre - signed up to it the day the OpenReach "Fibre broadband available here" sticker appeared on the cabinet at the end of my road - and I've had absolutely no problems in the 12 or so months I've had it - the connection is a pretty rock solid 40Mb down, 10Mb up.
Before that I was on Sky's copper offering and got a consistent 2.5Mb of the "up to 20Mb" I was paying for, but that is mostly a geographical issue and no other copper provider could have done any better - in fact Tiscali managed to do significantly worse on the same line which is what prompted the move to Sky in the first place.
In the Sky copper days I did manage to kill a couple of routers through overheating (my phone socket is down the back of my sofa by a radiator) but they were both replaced free of charge within a couple of days of a call to customer services with no quibbles, so what little customer services contact I've had with Sky has all been pretty positive.
My only experience with VM is them filling my recycling bin with dozens of flyers a month advertising tv and broadband services that I can't even have because I don't live in a cabled area!