"In fact, I don't even see a great deal of point in moving around providers, as they all use the same Openreach network anyway, and television programming is basically Sky or Freeview."
There are other variables. How secure is their customer information is a good starting point. Who provides customer support and from which continent is another.
And how about traffic shaping? One little gem from TT when they took over my previous provider was that they traffic-shaped nntp during the day. In fact they pretty well shaped it out of existence despite the fact that one of the services they'd taken over was Usenet provision.