So far, I have found 3 to be the best for customer service.
T-Mobile are atrocious.
( spangolin - the odds are good but the goods are odd, Fri 12 Jan 2007, 11:41, archived)

Christ no, 3 are terrible
They didn't send my mate's phone to him, but then wouldn't let him cancel the account until he returned the phone, so billed him for a non-existent phone! He's still trying to get his money back.
I never had any problem with Orange.
( Fergburger, Fri 12 Jan 2007, 11:51, archived)