We have fibre with BT. It was them or Sky (Plusnet is owned by BT and is a bit downgraded, although a bit cheaper). We also wanted BT Sport, which they threw in with the deal, although are now planning to charge extra for the Champions League football which is a cheek.
Recently had a problem and to my amazement, my email was answered! BT customer service is legendarily awful. A neighbour is with Virgin and says similar problem. Another neighbour has had a lot of negative issues with Talk Talk's reliability.
Not sure how good Sky are. If you're getting fibre, you'll want the one with the best router.
Anyone on here used a wifi extender? I just got one from BT and of course it doesn't work. Thick walls, so wifi is patchy in the bedroom, even for radio streaming.
Don't think BT do any retention deals. Sky do. It's pretty much always possible to get some sort of discount out of Sky when you are out of contract, just threaten to leave.
