i'm with virgin. not had many problems to be fair, but when you do its hard if not impossible to get a proper support response without jumping through umpteen hoops of stock emails responses etc etc "turn your router off and on" etc etc, unless you don't mind phoning an 0870 number. That's my only issue with them to be honest.
We're with Virgin. The connection sometimes stops for no reason* which is annoying, but when I have phoned the free 150(?) number the service has been great.