I originally had Sky for a few years then switched over to Virgin, primarily because I had broadband with them and they offered me a great deal for the TV package, broadband and phone. I find the V+ box excellent and customer service is normally quite good, however there are a few things I wished virgin had:
Sky Player - Virgin has no current service that allows you to watch your channels online although they might be introducing the Virgin player by the end of the year.
Sky Interactive - I have all the Sky Sports channels on Virgin, however sometimes Sky sports extra shows several games at once on that one channel, on Virgin this will default to one game whereas in Sky you have a selection of maybe four or more games, also access to fan zone, different angles, views etc.
Virgin doesn’t have any of the Sky Movie HD or Sky Sport HD channels, not sure if this will change
Virgin does have a very good catch-up on TV demand service and you have access to many shows and series free of charge also.
The only reason I lean towards virgin is because of the broadband if I was only interested in TV then I get Sky.