I've been with Virgin Media (formerly Blueyonder) for years. When it was Blueyonder it was without doubt the best internet you could get. Since the merger and branding it's gone steadily downhill.
A couple of years ago my connection started slowing down at peak times, becoming essentially unusable with packet loss and high erratic pings due to oversubscription, Virgin are generally very slow to sort these issues out, as it costs a lot of money to upgrade the UBRs for increased bandwidth. I had to complain to the Internet Service Providers Association to get the problem sorted, and got put in contact with Virgin's CEO's office, who finally got the problem fixed for me. I found out that as my area has a large student population they were torrenting 24/7 on the uncapped 50mbit service, which was causing problems for everyone in my area.
Now it's Virgin's fault for oversubscribing, but it's also some users fault for acting like gluttons at all-you-can-eat restaurants who grab every piece of pizza that appears and leaving crumbs for everyone else.
Fast forward two years, and after a recent upgrade to 20mbit I find the same issues AGAIN. The area is oversubscribed so online gaming in the evening is impossible due to the terrible pings and packet loss. Support confirm the oversubscription, and say the problem's not due to be fixed for THREE MONTHS.
I'd leave Virgin if I could but the fastest ADSL in my area is 2mbit.