I have just moved from Orange and their poor customer service. Now on O2 and getting twice the speed that I had with Orange. I am a long way from the exchange, so have to settle for a slower speed than most, so this increase is most welcome. I like the fact that there is an 0800 number to ring for support.
When I had a problem with Orange, I complained and they said "If you don't like it leave" So I did.
Great service so far with O2, kept well up to date with texts during the changeover, thumbs up from me.