It is all about experience, isn’t it?
For me, FD was so dependent on their (excellent) customer service that, when it seemed like it wasn’t working for me, there really wasn’t anything else worth staying for.
Conversely, I used to have a current account with N&P. They messed up a direct debt - but made the complaint and recovery process so good I stayed with them - and was a little upset when they decided to close the business.