I've been with 3 for about six years now. I was looking for a replacement for dreadful Vodafone service and opted for 3 purely because the woman in the shop gave me her personal phone number and said to call her if I had any problems - I thought this was exceptional customer service.
I haven't been disappointed with the choice: it's not the cheapest but pretty good value for money, the At Home service is great, the reception is excellent (I believe it has the widest coverage); there's a good choice of phones and when I have had a problem, it's been solved really quickly. I can't see any reasons to change
