I chose Zen because of their high rating with customer service. I have to say I have not been disappointed so far. The service has been without issues, especially since going to full fibre a couple of years ago.
The only disappointment (which is not really down to customer service, and which affects the value for money rating), is that their digital voice requires (officially at least) to have the Fritz! router they send you, as the first device connected to the OpenReach modem (instead of giving out your SIP credentials, so that you can use the VoIP service with whichever phone/app you want, like almost every other SIP provider). This meant that I had to switch my landline to another VoIP provider (which turned out to be cheaper).
Time With Provider: 230 Weeks
Package Name: Full Fibre 900