I joined PlusNet in a different guise many years ago - they are also one of the 2 Waitrose ISPs (though only Greenbee still accepts new accounts)

So when I switched over, I asked to keep my Waitrose email addresses - their answer explains why I still use this.

We have worked up from having a 20GB ceiling on monthly downloads (it doesn't work - I have three teens at home) through unlimited to go-faster fibre broadband. Each step has led to a tariff that has been reduced by an introductory offer, phone and online support well into the evening and prompt email and online updates that have meant that downtime beats the office figure (which is impressive).

To date, I have been able to discuss issues at a level that makes sense to me - though not a network specialist, I have some grasp of what I'm dealing with. And, up until the switch to fibre, was running Netgear kit of my choosing.
The domestic network has been looked at by the BT engineers - who have been helpful in providing tips on re-use as time has gone by.

The service itself is there when I need it - which isn't very often. The support from BT some time takes a little organising, but all time-scales have been adhered to and I have few complaints. Prices are competitive and I have had fewer run-ins than friends who use BT, Sky or Virgin - something I find quite reassuring!

I think you sometimes need to look beyond the cost to consider quality-of-service. And these guys take some beating.