I'm with Nationwide and they've done nothing in 10years to offend me. Which I suppose is what you need from a bank.
I had months of grief with Nationwide a couple of years ago. Months of it, over a simple thing like replacing a debit card.
The major issues were never getting to speak to the same person twice to sort it out, and their refusal to send a new card to my work address, or to a Nationwide branch. They insisted on sending it by courier to my home, time after time, but of course I was never in as I have a job!
I switched to Halifax, and I've had no problems with them. Internet banking is fine, and branches open in London early enough for me to pop in on the way to work if I need to.