I would not recommend Virgin Media unless it is a choice between them or ADSL below 5Mb/s.
As mentioned, support is rather pooo via phone and twitter... they just refer you to online troubleshooting guides or read these out over the phone, and also might find some things that work very well on ADSL/VDSL might not work all too well on Virgin Media due to the method of connectivity to their network.
If you currently happy with the service you receive from Sky, I would stay with them, I have seen some good reviews of there broadband recently and my experiences of sky's broadband services have been and continue to be very good.
Hope this information serves you well
UPDATE: Thought I should mention that not all Virgin Media's support is oversea's but have found there Technical Support to be mostly overseas, billing and accounts are UK though!
Also service reliability and consistency will rely on your local networks capacity and usage,
I've currently got a couple of Virgin Media connections and they seem to fair well but the area they are in is notoriously a very good network with Virgin Media favouring it in some trials of faster services in the past and is currently being used in a trial of there new public hotspots features.
However I've also had services in an area of "over-utilisation" where speeds can go from 160Mb/s during the day to 2Mb/s in the evening and any usability of the connection after 5PM was impossible,
For the last 3 months of service from Virgin Media we was forced to rely on EE's 100GB Sim Card offers heavily.... and the fact that gaming online was far superior via a mobile network than a "Superfast fibre broadband" connection was interesting!
Edited by mlmclaren (Fri 04-Sep-15 11:18:14)