I moved from Plusnert to BT Infinity 1 + BT sports TV in March.
I've disliked BT for many years, since I used them for dial up in the 90's, so I was very wary of going to them but I must say I've had no problems whatsoever. The sync speed is, as you would expect, the same as with PN and if anything the through put is slightly better.
I would advice to keep a eye on their deals to time placing the order, they seem to change each week some weeks being much better than others. Also order through a cash back site you can get loads of ££ back.
My deal:
Unlimited Infinity 1 + BT sports TV £10 / month
Line rental + free caller display £17.99 / month
Received a BT debit card pre loaded with £100
Cashback from topcashback.co.uk £199
All my outgoing calls are through VOIP so I haven't looked at call tariffs.
It's a 12 month contract, I don't know what deals they do for the second year.