From what I've been reading sky fibre is the best. Virgin apparently has latency issues and poor upload speeds, and they also have a problem with traffic at peak times which caps whatever internet package you have anyway.
It's their superhubs, they have a latency like the superhub 3 I use. My gaming is fine with little delay but the more matches I play the worse the latency gets (as worse as seconds behind other players) which is unbearable. My guess is the superhubs are the issue, they're not stable enough, but hopefully they fix it but then again I've had this issue for 2 years