Sky and Virgin seem good for a few months, Sky having by far the better interface of the two. Virgin's so bad that I wouldn't have it. You soon realise the same stuff is coming around and around and around and around over and over again, particularly on the documentary channels.
A hell of a lot of the channel's content is bought in from the BBC and ITV – Discovery's motoring channel is still showing Deals on Wheels etc. The big deal in my view is that you get the really good stuff from HBO before anyone else, which might be worth the subscription for you.
The good stuff does, however, eventually find its way to terrestrial, but is often broadcast at terrible times. The Wire was on the BBC at stupid o'clock at night for example.
End result is, I find that with a PVR, I can record more decent stuff from Freeview than I have the time to watch.